Abstract

Methanol is the prototypical intermediate C3V barrier to the internal rotation molecule. It is also one of the primary sources of line confusion in the interstellar medium where it is observed in a variety of regions with temperatures approaching room temperature in the more extreme cases. Recently, a fairly comprehensive rotational study of methanol was performed that analyzed the available data to J=30 in the first three torsional states with a rho axis method (RAM) Hamiltonian. The availability of a new frequency source covering 2.48 to 2.77THz offered a unique opportunity to rigorously test the ability of the RAM Hamiltonian model in extrapolation in both J and K quantum numbers and an opportunity to confirm a number of newly assigned methanol levels. It also facilitated a unique opportunity for a direct comparison of results obtained with a frequency multiplier, Fourier transform infrared, laser sideband, tunable far infrared, and quantum cascade lasers at terahertz frequencies. The spectrum of methanol is presented and assigned for the 2.482.77THz band. Lines in the first four torsional states are identified and compared to predictions of the RAM model for the first three torsional states and available energy levels for the vt=3 state. A number of previously unidentified subbands are assigned for the first time, providing some unique insight into the difficulties of extrapolating with a rho axis C3V internal rotation Hamiltonian.

© 2011 Optical Society of America

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2011 (2)

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

R. M. Lees, L.-H. Xu, B. E. Billinghurst, and D. R. T. Appadoo, “Weeding the cosmos--FIR synchrotron spectroscopy of methanol at the Canadian Light Source,” J. Mol. Structr. 993, 269-276 (2011).
[CrossRef]

2010 (2)

H. Richter, S. G. Pavlov, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, D. A. Ritchie, and H.-W. Hübers, “Submegahertz frequency stabilization of a terahertz quantum cascade laser to a molecular absorption line,” Appl. Phys. Lett. 96, 071112(2010).
[CrossRef]

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, A. Bell, B. Klein, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne spectrometer using a quantum cascade laser,” Appl. Phys. Lett. 97, 161105 (2010).
[CrossRef]

2009 (1)

J. C. Pearson, C. S. Brauer, B. J. Drouin, and L.-H. Xu, “The rotational spectrum of methanol in the third excited torsional state,” Can. J. Phys. 87, 449-467 (2009).
[CrossRef]

2008 (1)

L.-H. Xu, J. Fisher, R. M. Lees, H. Y. Shi, J. T. Hougen, J. C. Pearson, B. J. Drouin, G. A. Blake, and R. Braakman, “Torsion-rotation global analysis of the first three torsional states (vt=0, 1, 2) and terahertz database for methanol,” J. Mol. Spectrosc. 251, 305-313 (2008).
[CrossRef]

2007 (1)

H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “Molecular spectroscopy with terahertz quantum cascade lasers,” J. Nanoelectron. Optoelectron. 2, 101-107 (2007).
[CrossRef]

2006 (1)

H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser,” Appl. Phys. Lett. 89, 061115(2006).
[CrossRef]

2005 (3)

B. J. Drouin, F. W. Maiwald, and J. C. Pearson, “Application of cascaded frequency multiplication to molecular spectroscopy,” Rev. Sci. Instrum. 76, 093113 (2005).
[CrossRef]

H. S. P. Müller, F. Schlöder, J. Stutzki, and G. Winnewisser, “The Cologne database for molecular spectroscopy, CDMS: a useful tool for astronomers and spectroscopists,” J. Mol. Structr. 742, 215-227 (2005).
[CrossRef]

D. M. Cragg, A. M. Sobolev, and P. D. Godfrey, “Models of class II methanol masers based on improved molecular data,” Mon. Not. R. Astron. Soc. 360, 533-545 (2005).
[CrossRef]

2004 (1)

S. Leurini, P. Schilke, K. M. Menten, D. R. Flower, J. T. Pottage, and L.-H. Xu, “Methanol as a diagnostic tool of interstellar clouds--I. Model calculations and application to molecular clouds,” Astron. Astrophys. 422, 573-585 (2004).
[CrossRef]

2001 (1)

H. Wang, L. Samoska, T. Gaier, A. Peralta, H.-H. Liao, Y. C. Leong, S. Weinreb, Y. C. Chen, M. Nishimoto, and R. Lai, “Power-amplifier modules covering 70-113 GHzusing MMICs,” IEEE Trans. Microw. Theory Tech. 49, 9-16(2001).
[CrossRef]

2000 (1)

R. Gendriesch, F. Lewen, G. Winnewisser, and J. Hahn, “Precision broadband spectroscopy near 2 THz: frequency-stabilized laser sideband spectrometer with backward-wave oscillators,” J. Mol. Spectrosc. 203, 205-207 (2000).
[CrossRef] [PubMed]

1999 (1)

P. H. Siegel, R. P. Smith, M. C. Gaidis, and S. C. Martin, “2.5 THz GaAs monolithic membrane-diode mixer,” IEEE Trans. Microw. Theory Tech. 47, 596-604 (1999).
[CrossRef]

1997 (1)

H. M. Pickett, “Theoretical studies of internal rotation for an asymmetric top,” J. Chem. Phys. 107, 6732-6735(1997).
[CrossRef]

1994 (2)

F. Matsushima, K. M. Evenson, and L. R. Zink, “Absolute frequency measurements of methanol from 1.5 to 6.5 THz,” J. Mol. Spectrosc. 164, 517-530 (1994).
[CrossRef]

J. T. Hougen, I. Kleiner, and M. Godefroid, “Selection-rules and intensity calculations for a CS asymmetric-top molecule containing a methyl-group internal rotor,” J. Mol. Spectrosc. 163, 559-586 (1994).
[CrossRef]

1992 (2)

T. D. Varberg and K. M. Evenson, “Accurate far-infrared rotational frequencies of carbon monoxide,” Astrophys. J. 385, 763-765 (1992).
[CrossRef]

T. Anderson, E. Herbst, and F. C. De Lucia, “An extension of the high-resolution millimeter- and submillimeter-wave spectrum of methanol to high angular momentum quantum numbers,” Astrophys. J. Suppl. Ser. 82, 405-444 (1992).
[CrossRef]

1991 (1)

K. M. Menten, “The discovery of a new, very strong, and widespread interstellar methanol maser line,” Astrophys. J. 380, L75-L78 (1991).
[CrossRef]

1987 (1)

W. Batrla, H. E. Matthews, K. M. Menten, and C. M. Walmsley, “Detection of strong methanol masers towards galactic H II regions,” Nature 326, 49-51 (1987).
[CrossRef]

1984 (1)

K. V. L. N. Sastry, R. M. Lees, and F. C. De Lucia, “Microwave and submillimeter-wave spectra of CH3OH,” J. Mol. Spectrosc. 103, 486-494 (1984).
[CrossRef]

1962 (1)

B. Kirtman, “Interactions between ordinary vibrations and hindered internal rotation. I. Rotational energies,” J. Chem. Phys. 37, 2516-2539 (1962).
[CrossRef]

Anderson, T.

T. Anderson, E. Herbst, and F. C. De Lucia, “An extension of the high-resolution millimeter- and submillimeter-wave spectrum of methanol to high angular momentum quantum numbers,” Astrophys. J. Suppl. Ser. 82, 405-444 (1992).
[CrossRef]

Appadoo, D. R. T.

R. M. Lees, L.-H. Xu, B. E. Billinghurst, and D. R. T. Appadoo, “Weeding the cosmos--FIR synchrotron spectroscopy of methanol at the Canadian Light Source,” J. Mol. Structr. 993, 269-276 (2011).
[CrossRef]

Batrla, W.

W. Batrla, H. E. Matthews, K. M. Menten, and C. M. Walmsley, “Detection of strong methanol masers towards galactic H II regions,” Nature 326, 49-51 (1987).
[CrossRef]

Beere, H. E.

H. Richter, S. G. Pavlov, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, D. A. Ritchie, and H.-W. Hübers, “Submegahertz frequency stabilization of a terahertz quantum cascade laser to a molecular absorption line,” Appl. Phys. Lett. 96, 071112(2010).
[CrossRef]

H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “Molecular spectroscopy with terahertz quantum cascade lasers,” J. Nanoelectron. Optoelectron. 2, 101-107 (2007).
[CrossRef]

H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser,” Appl. Phys. Lett. 89, 061115(2006).
[CrossRef]

Bell, A.

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, A. Bell, B. Klein, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne spectrometer using a quantum cascade laser,” Appl. Phys. Lett. 97, 161105 (2010).
[CrossRef]

Bell, T. A.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Bergin, E. A.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Billinghurst, B. E.

R. M. Lees, L.-H. Xu, B. E. Billinghurst, and D. R. T. Appadoo, “Weeding the cosmos--FIR synchrotron spectroscopy of methanol at the Canadian Light Source,” J. Mol. Structr. 993, 269-276 (2011).
[CrossRef]

Blake, G. A.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

L.-H. Xu, J. Fisher, R. M. Lees, H. Y. Shi, J. T. Hougen, J. C. Pearson, B. J. Drouin, G. A. Blake, and R. Braakman, “Torsion-rotation global analysis of the first three torsional states (vt=0, 1, 2) and terahertz database for methanol,” J. Mol. Spectrosc. 251, 305-313 (2008).
[CrossRef]

Braakman, R.

L.-H. Xu, J. Fisher, R. M. Lees, H. Y. Shi, J. T. Hougen, J. C. Pearson, B. J. Drouin, G. A. Blake, and R. Braakman, “Torsion-rotation global analysis of the first three torsional states (vt=0, 1, 2) and terahertz database for methanol,” J. Mol. Spectrosc. 251, 305-313 (2008).
[CrossRef]

Brauer, C. S.

J. C. Pearson, C. S. Brauer, B. J. Drouin, and L.-H. Xu, “The rotational spectrum of methanol in the third excited torsional state,” Can. J. Phys. 87, 449-467 (2009).
[CrossRef]

Caux, E.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Ceccarelli, C.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Cernicharo, J.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Chattopadhyay, G.

J. C. Pearson, B. J. Drouin, A. Maestrini, I. Mehdi, J. Ward, R. H. Lin, S. Yu, J. J. Gill, B. Thomas, C. Lee, G. Chattopadhyay, E. Schlecht, F. W. Maiwald, P. F. Goldsmith, and P. Siegel, “Demonstration of a room temperature 2.48-2.75 THz coherent spectroscopy source,” Rev. Sci. Instrum. (to be published).
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Chen, Y. C.

H. Wang, L. Samoska, T. Gaier, A. Peralta, H.-H. Liao, Y. C. Leong, S. Weinreb, Y. C. Chen, M. Nishimoto, and R. Lai, “Power-amplifier modules covering 70-113 GHzusing MMICs,” IEEE Trans. Microw. Theory Tech. 49, 9-16(2001).
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Comito, C.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
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D. M. Cragg, A. M. Sobolev, and P. D. Godfrey, “Models of class II methanol masers based on improved molecular data,” Mon. Not. R. Astron. Soc. 360, 533-545 (2005).
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Crockett, N. R.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
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Daniel, F.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
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T. Anderson, E. Herbst, and F. C. De Lucia, “An extension of the high-resolution millimeter- and submillimeter-wave spectrum of methanol to high angular momentum quantum numbers,” Astrophys. J. Suppl. Ser. 82, 405-444 (1992).
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K. V. L. N. Sastry, R. M. Lees, and F. C. De Lucia, “Microwave and submillimeter-wave spectra of CH3OH,” J. Mol. Spectrosc. 103, 486-494 (1984).
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J. C. Pearson, C. S. Brauer, B. J. Drouin, and L.-H. Xu, “The rotational spectrum of methanol in the third excited torsional state,” Can. J. Phys. 87, 449-467 (2009).
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L.-H. Xu, J. Fisher, R. M. Lees, H. Y. Shi, J. T. Hougen, J. C. Pearson, B. J. Drouin, G. A. Blake, and R. Braakman, “Torsion-rotation global analysis of the first three torsional states (vt=0, 1, 2) and terahertz database for methanol,” J. Mol. Spectrosc. 251, 305-313 (2008).
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B. J. Drouin, F. W. Maiwald, and J. C. Pearson, “Application of cascaded frequency multiplication to molecular spectroscopy,” Rev. Sci. Instrum. 76, 093113 (2005).
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J. C. Pearson, B. J. Drouin, A. Maestrini, I. Mehdi, J. Ward, R. H. Lin, S. Yu, J. J. Gill, B. Thomas, C. Lee, G. Chattopadhyay, E. Schlecht, F. W. Maiwald, P. F. Goldsmith, and P. Siegel, “Demonstration of a room temperature 2.48-2.75 THz coherent spectroscopy source,” Rev. Sci. Instrum. (to be published).
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Dubernet, M.-L.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
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S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Encrenaz, P.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
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T. D. Varberg and K. M. Evenson, “Accurate far-infrared rotational frequencies of carbon monoxide,” Astrophys. J. 385, 763-765 (1992).
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L.-H. Xu, J. Fisher, R. M. Lees, H. Y. Shi, J. T. Hougen, J. C. Pearson, B. J. Drouin, G. A. Blake, and R. Braakman, “Torsion-rotation global analysis of the first three torsional states (vt=0, 1, 2) and terahertz database for methanol,” J. Mol. Spectrosc. 251, 305-313 (2008).
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S. Leurini, P. Schilke, K. M. Menten, D. R. Flower, J. T. Pottage, and L.-H. Xu, “Methanol as a diagnostic tool of interstellar clouds--I. Model calculations and application to molecular clouds,” Astron. Astrophys. 422, 573-585 (2004).
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P. H. Siegel, R. P. Smith, M. C. Gaidis, and S. C. Martin, “2.5 THz GaAs monolithic membrane-diode mixer,” IEEE Trans. Microw. Theory Tech. 47, 596-604 (1999).
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Gaier, T.

H. Wang, L. Samoska, T. Gaier, A. Peralta, H.-H. Liao, Y. C. Leong, S. Weinreb, Y. C. Chen, M. Nishimoto, and R. Lai, “Power-amplifier modules covering 70-113 GHzusing MMICs,” IEEE Trans. Microw. Theory Tech. 49, 9-16(2001).
[CrossRef]

Gao, J. R.

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, A. Bell, B. Klein, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne spectrometer using a quantum cascade laser,” Appl. Phys. Lett. 97, 161105 (2010).
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R. Gendriesch, F. Lewen, G. Winnewisser, and J. Hahn, “Precision broadband spectroscopy near 2 THz: frequency-stabilized laser sideband spectrometer with backward-wave oscillators,” J. Mol. Spectrosc. 203, 205-207 (2000).
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Gerin, M.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

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S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Gill, J. J.

J. C. Pearson, B. J. Drouin, A. Maestrini, I. Mehdi, J. Ward, R. H. Lin, S. Yu, J. J. Gill, B. Thomas, C. Lee, G. Chattopadhyay, E. Schlecht, F. W. Maiwald, P. F. Goldsmith, and P. Siegel, “Demonstration of a room temperature 2.48-2.75 THz coherent spectroscopy source,” Rev. Sci. Instrum. (to be published).
[CrossRef]

Godefroid, M.

J. T. Hougen, I. Kleiner, and M. Godefroid, “Selection-rules and intensity calculations for a CS asymmetric-top molecule containing a methyl-group internal rotor,” J. Mol. Spectrosc. 163, 559-586 (1994).
[CrossRef]

Godfrey, P. D.

D. M. Cragg, A. M. Sobolev, and P. D. Godfrey, “Models of class II methanol masers based on improved molecular data,” Mon. Not. R. Astron. Soc. 360, 533-545 (2005).
[CrossRef]

Goicoechea, J. R.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Goldsmith, P. F.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

J. C. Pearson, B. J. Drouin, A. Maestrini, I. Mehdi, J. Ward, R. H. Lin, S. Yu, J. J. Gill, B. Thomas, C. Lee, G. Chattopadhyay, E. Schlecht, F. W. Maiwald, P. F. Goldsmith, and P. Siegel, “Demonstration of a room temperature 2.48-2.75 THz coherent spectroscopy source,” Rev. Sci. Instrum. (to be published).
[CrossRef]

Gupta, H.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Hahn, J.

R. Gendriesch, F. Lewen, G. Winnewisser, and J. Hahn, “Precision broadband spectroscopy near 2 THz: frequency-stabilized laser sideband spectrometer with backward-wave oscillators,” J. Mol. Spectrosc. 203, 205-207 (2000).
[CrossRef] [PubMed]

Herbst, E.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

T. Anderson, E. Herbst, and F. C. De Lucia, “An extension of the high-resolution millimeter- and submillimeter-wave spectrum of methanol to high angular momentum quantum numbers,” Astrophys. J. Suppl. Ser. 82, 405-444 (1992).
[CrossRef]

Higgins, R.

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, A. Bell, B. Klein, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne spectrometer using a quantum cascade laser,” Appl. Phys. Lett. 97, 161105 (2010).
[CrossRef]

Hougen, J. T.

L.-H. Xu, J. Fisher, R. M. Lees, H. Y. Shi, J. T. Hougen, J. C. Pearson, B. J. Drouin, G. A. Blake, and R. Braakman, “Torsion-rotation global analysis of the first three torsional states (vt=0, 1, 2) and terahertz database for methanol,” J. Mol. Spectrosc. 251, 305-313 (2008).
[CrossRef]

J. T. Hougen, I. Kleiner, and M. Godefroid, “Selection-rules and intensity calculations for a CS asymmetric-top molecule containing a methyl-group internal rotor,” J. Mol. Spectrosc. 163, 559-586 (1994).
[CrossRef]

Hovenier, J. N.

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, A. Bell, B. Klein, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne spectrometer using a quantum cascade laser,” Appl. Phys. Lett. 97, 161105 (2010).
[CrossRef]

Hu, Q.

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, A. Bell, B. Klein, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne spectrometer using a quantum cascade laser,” Appl. Phys. Lett. 97, 161105 (2010).
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Hübers, H.-W.

H. Richter, S. G. Pavlov, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, D. A. Ritchie, and H.-W. Hübers, “Submegahertz frequency stabilization of a terahertz quantum cascade laser to a molecular absorption line,” Appl. Phys. Lett. 96, 071112(2010).
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H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “Molecular spectroscopy with terahertz quantum cascade lasers,” J. Nanoelectron. Optoelectron. 2, 101-107 (2007).
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H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser,” Appl. Phys. Lett. 89, 061115(2006).
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Joblin, C.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Johnstone, D.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
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Kirtman, B.

B. Kirtman, “Interactions between ordinary vibrations and hindered internal rotation. I. Rotational energies,” J. Chem. Phys. 37, 2516-2539 (1962).
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S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
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[CrossRef]

L.-H. Xu, J. Fisher, R. M. Lees, H. Y. Shi, J. T. Hougen, J. C. Pearson, B. J. Drouin, G. A. Blake, and R. Braakman, “Torsion-rotation global analysis of the first three torsional states (vt=0, 1, 2) and terahertz database for methanol,” J. Mol. Spectrosc. 251, 305-313 (2008).
[CrossRef]

B. J. Drouin, F. W. Maiwald, and J. C. Pearson, “Application of cascaded frequency multiplication to molecular spectroscopy,” Rev. Sci. Instrum. 76, 093113 (2005).
[CrossRef]

J. C. Pearson, B. J. Drouin, A. Maestrini, I. Mehdi, J. Ward, R. H. Lin, S. Yu, J. J. Gill, B. Thomas, C. Lee, G. Chattopadhyay, E. Schlecht, F. W. Maiwald, P. F. Goldsmith, and P. Siegel, “Demonstration of a room temperature 2.48-2.75 THz coherent spectroscopy source,” Rev. Sci. Instrum. (to be published).
[CrossRef]

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H. Wang, L. Samoska, T. Gaier, A. Peralta, H.-H. Liao, Y. C. Leong, S. Weinreb, Y. C. Chen, M. Nishimoto, and R. Lai, “Power-amplifier modules covering 70-113 GHzusing MMICs,” IEEE Trans. Microw. Theory Tech. 49, 9-16(2001).
[CrossRef]

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S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
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[CrossRef]

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S. Leurini, P. Schilke, K. M. Menten, D. R. Flower, J. T. Pottage, and L.-H. Xu, “Methanol as a diagnostic tool of interstellar clouds--I. Model calculations and application to molecular clouds,” Astron. Astrophys. 422, 573-585 (2004).
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S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
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H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser,” Appl. Phys. Lett. 89, 061115(2006).
[CrossRef]

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H. Richter, S. G. Pavlov, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, D. A. Ritchie, and H.-W. Hübers, “Submegahertz frequency stabilization of a terahertz quantum cascade laser to a molecular absorption line,” Appl. Phys. Lett. 96, 071112(2010).
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H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “Molecular spectroscopy with terahertz quantum cascade lasers,” J. Nanoelectron. Optoelectron. 2, 101-107 (2007).
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H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser,” Appl. Phys. Lett. 89, 061115(2006).
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[CrossRef]

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[CrossRef]

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J. C. Pearson, B. J. Drouin, A. Maestrini, I. Mehdi, J. Ward, R. H. Lin, S. Yu, J. J. Gill, B. Thomas, C. Lee, G. Chattopadhyay, E. Schlecht, F. W. Maiwald, P. F. Goldsmith, and P. Siegel, “Demonstration of a room temperature 2.48-2.75 THz coherent spectroscopy source,” Rev. Sci. Instrum. (to be published).
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S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
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[CrossRef]

H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “Molecular spectroscopy with terahertz quantum cascade lasers,” J. Nanoelectron. Optoelectron. 2, 101-107 (2007).
[CrossRef]

H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser,” Appl. Phys. Lett. 89, 061115(2006).
[CrossRef]

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L.-H. Xu, J. Fisher, R. M. Lees, H. Y. Shi, J. T. Hougen, J. C. Pearson, B. J. Drouin, G. A. Blake, and R. Braakman, “Torsion-rotation global analysis of the first three torsional states (vt=0, 1, 2) and terahertz database for methanol,” J. Mol. Spectrosc. 251, 305-313 (2008).
[CrossRef]

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Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, A. Bell, B. Klein, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne spectrometer using a quantum cascade laser,” Appl. Phys. Lett. 97, 161105 (2010).
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S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

H. S. P. Müller, F. Schlöder, J. Stutzki, and G. Winnewisser, “The Cologne database for molecular spectroscopy, CDMS: a useful tool for astronomers and spectroscopists,” J. Mol. Structr. 742, 215-227 (2005).
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J. C. Pearson, B. J. Drouin, A. Maestrini, I. Mehdi, J. Ward, R. H. Lin, S. Yu, J. J. Gill, B. Thomas, C. Lee, G. Chattopadhyay, E. Schlecht, F. W. Maiwald, P. F. Goldsmith, and P. Siegel, “Demonstration of a room temperature 2.48-2.75 THz coherent spectroscopy source,” Rev. Sci. Instrum. (to be published).
[CrossRef]

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S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

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H. Richter, S. G. Pavlov, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, D. A. Ritchie, and H.-W. Hübers, “Submegahertz frequency stabilization of a terahertz quantum cascade laser to a molecular absorption line,” Appl. Phys. Lett. 96, 071112(2010).
[CrossRef]

H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “Molecular spectroscopy with terahertz quantum cascade lasers,” J. Nanoelectron. Optoelectron. 2, 101-107 (2007).
[CrossRef]

H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser,” Appl. Phys. Lett. 89, 061115(2006).
[CrossRef]

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H. Wang, L. Samoska, T. Gaier, A. Peralta, H.-H. Liao, Y. C. Leong, S. Weinreb, Y. C. Chen, M. Nishimoto, and R. Lai, “Power-amplifier modules covering 70-113 GHzusing MMICs,” IEEE Trans. Microw. Theory Tech. 49, 9-16(2001).
[CrossRef]

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S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
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Ward, J.

J. C. Pearson, B. J. Drouin, A. Maestrini, I. Mehdi, J. Ward, R. H. Lin, S. Yu, J. J. Gill, B. Thomas, C. Lee, G. Chattopadhyay, E. Schlecht, F. W. Maiwald, P. F. Goldsmith, and P. Siegel, “Demonstration of a room temperature 2.48-2.75 THz coherent spectroscopy source,” Rev. Sci. Instrum. (to be published).
[CrossRef]

Weinreb, S.

H. Wang, L. Samoska, T. Gaier, A. Peralta, H.-H. Liao, Y. C. Leong, S. Weinreb, Y. C. Chen, M. Nishimoto, and R. Lai, “Power-amplifier modules covering 70-113 GHzusing MMICs,” IEEE Trans. Microw. Theory Tech. 49, 9-16(2001).
[CrossRef]

Williams, B. S.

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, A. Bell, B. Klein, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne spectrometer using a quantum cascade laser,” Appl. Phys. Lett. 97, 161105 (2010).
[CrossRef]

Winnewisser, B. P.

G. Moruzzi, B. P. Winnewisser, M. Winnewisser, I. Mukhopadhyay, and F. Struma, Microwave, Infrared and Laser Transitions of Methanol, Atlas of Assigned Lines from 0 to 1258 cm−1 (CRC Press, 1995).
[PubMed]

Winnewisser, G.

H. S. P. Müller, F. Schlöder, J. Stutzki, and G. Winnewisser, “The Cologne database for molecular spectroscopy, CDMS: a useful tool for astronomers and spectroscopists,” J. Mol. Structr. 742, 215-227 (2005).
[CrossRef]

R. Gendriesch, F. Lewen, G. Winnewisser, and J. Hahn, “Precision broadband spectroscopy near 2 THz: frequency-stabilized laser sideband spectrometer with backward-wave oscillators,” J. Mol. Spectrosc. 203, 205-207 (2000).
[CrossRef] [PubMed]

Winnewisser, M.

G. Moruzzi, B. P. Winnewisser, M. Winnewisser, I. Mukhopadhyay, and F. Struma, Microwave, Infrared and Laser Transitions of Methanol, Atlas of Assigned Lines from 0 to 1258 cm−1 (CRC Press, 1995).
[PubMed]

Xu, L.-H.

R. M. Lees, L.-H. Xu, B. E. Billinghurst, and D. R. T. Appadoo, “Weeding the cosmos--FIR synchrotron spectroscopy of methanol at the Canadian Light Source,” J. Mol. Structr. 993, 269-276 (2011).
[CrossRef]

J. C. Pearson, C. S. Brauer, B. J. Drouin, and L.-H. Xu, “The rotational spectrum of methanol in the third excited torsional state,” Can. J. Phys. 87, 449-467 (2009).
[CrossRef]

L.-H. Xu, J. Fisher, R. M. Lees, H. Y. Shi, J. T. Hougen, J. C. Pearson, B. J. Drouin, G. A. Blake, and R. Braakman, “Torsion-rotation global analysis of the first three torsional states (vt=0, 1, 2) and terahertz database for methanol,” J. Mol. Spectrosc. 251, 305-313 (2008).
[CrossRef]

S. Leurini, P. Schilke, K. M. Menten, D. R. Flower, J. T. Pottage, and L.-H. Xu, “Methanol as a diagnostic tool of interstellar clouds--I. Model calculations and application to molecular clouds,” Astron. Astrophys. 422, 573-585 (2004).
[CrossRef]

Yorke, H. W.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Yu, S.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

J. C. Pearson, B. J. Drouin, A. Maestrini, I. Mehdi, J. Ward, R. H. Lin, S. Yu, J. J. Gill, B. Thomas, C. Lee, G. Chattopadhyay, E. Schlecht, F. W. Maiwald, P. F. Goldsmith, and P. Siegel, “Demonstration of a room temperature 2.48-2.75 THz coherent spectroscopy source,” Rev. Sci. Instrum. (to be published).
[CrossRef]

Zink, L. R.

F. Matsushima, K. M. Evenson, and L. R. Zink, “Absolute frequency measurements of methanol from 1.5 to 6.5 THz,” J. Mol. Spectrosc. 164, 517-530 (1994).
[CrossRef]

Zmuidzinas, J.

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Appl. Phys. Lett. (3)

H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “High-resolution gas phase spectroscopy with a distributed feedback terahertz quantum cascade laser,” Appl. Phys. Lett. 89, 061115(2006).
[CrossRef]

H. Richter, S. G. Pavlov, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, D. A. Ritchie, and H.-W. Hübers, “Submegahertz frequency stabilization of a terahertz quantum cascade laser to a molecular absorption line,” Appl. Phys. Lett. 96, 071112(2010).
[CrossRef]

Y. Ren, J. N. Hovenier, R. Higgins, J. R. Gao, T. M. Klapwijk, S. C. Shi, A. Bell, B. Klein, B. S. Williams, S. Kumar, Q. Hu, and J. L. Reno, “Terahertz heterodyne spectrometer using a quantum cascade laser,” Appl. Phys. Lett. 97, 161105 (2010).
[CrossRef]

Astron. Astrophys. (2)

S. Leurini, P. Schilke, K. M. Menten, D. R. Flower, J. T. Pottage, and L.-H. Xu, “Methanol as a diagnostic tool of interstellar clouds--I. Model calculations and application to molecular clouds,” Astron. Astrophys. 422, 573-585 (2004).
[CrossRef]

S. Wang, E. A. Bergin, and N. R. Crockett,P. F. Goldsmith, D. C. Lis, J. C. Pearson, P. Schilke, T. A. Bell, C. Comito, G. A. Blake, E. Caux, C. Ceccarelli, J. Cernicharo, F. Daniel, M.-L. Dubernet, M. Emprechtinger, P. Encrenaz, M. Gerin, T. F. Giesen, J. R. Goicoechea, H. Gupta, E. Herbst, C. Joblin, D. Johnstone, W. D. Langer, W. B. Latter, S. D. Lord, S. Maret, P. G. Martin, G. J. Melnick, K. M. Menten, P. Morris, H. S. P. Müller, J. A. Murphy, D. A. Neufeld, V. Ossenkopf, M. Pérault, T. G. Phillips, R. Plume, S.-L. Qin, S. Schlemmer, J. Stutzki, N. Trappe, F. F. S. van der Tak, C. Vastel, H. W. Yorke, S. Yu, and J. Zmuidzinas, “Herschel observations of EXtra-Ordinary Sources (HEXOS): methanol as a probe of physical conditions in Orion KL,” Astron. Astrophys. 527, A95 (2011).
[CrossRef]

Astrophys. J. (2)

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[CrossRef]

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[CrossRef]

Astrophys. J. Suppl. Ser. (1)

T. Anderson, E. Herbst, and F. C. De Lucia, “An extension of the high-resolution millimeter- and submillimeter-wave spectrum of methanol to high angular momentum quantum numbers,” Astrophys. J. Suppl. Ser. 82, 405-444 (1992).
[CrossRef]

Can. J. Phys. (1)

J. C. Pearson, C. S. Brauer, B. J. Drouin, and L.-H. Xu, “The rotational spectrum of methanol in the third excited torsional state,” Can. J. Phys. 87, 449-467 (2009).
[CrossRef]

IEEE Trans. Microw. Theory Tech. (2)

P. H. Siegel, R. P. Smith, M. C. Gaidis, and S. C. Martin, “2.5 THz GaAs monolithic membrane-diode mixer,” IEEE Trans. Microw. Theory Tech. 47, 596-604 (1999).
[CrossRef]

H. Wang, L. Samoska, T. Gaier, A. Peralta, H.-H. Liao, Y. C. Leong, S. Weinreb, Y. C. Chen, M. Nishimoto, and R. Lai, “Power-amplifier modules covering 70-113 GHzusing MMICs,” IEEE Trans. Microw. Theory Tech. 49, 9-16(2001).
[CrossRef]

J. Chem. Phys. (2)

H. M. Pickett, “Theoretical studies of internal rotation for an asymmetric top,” J. Chem. Phys. 107, 6732-6735(1997).
[CrossRef]

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[CrossRef]

J. Mol. Spectrosc. (5)

R. Gendriesch, F. Lewen, G. Winnewisser, and J. Hahn, “Precision broadband spectroscopy near 2 THz: frequency-stabilized laser sideband spectrometer with backward-wave oscillators,” J. Mol. Spectrosc. 203, 205-207 (2000).
[CrossRef] [PubMed]

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[CrossRef]

F. Matsushima, K. M. Evenson, and L. R. Zink, “Absolute frequency measurements of methanol from 1.5 to 6.5 THz,” J. Mol. Spectrosc. 164, 517-530 (1994).
[CrossRef]

L.-H. Xu, J. Fisher, R. M. Lees, H. Y. Shi, J. T. Hougen, J. C. Pearson, B. J. Drouin, G. A. Blake, and R. Braakman, “Torsion-rotation global analysis of the first three torsional states (vt=0, 1, 2) and terahertz database for methanol,” J. Mol. Spectrosc. 251, 305-313 (2008).
[CrossRef]

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[CrossRef]

J. Mol. Structr. (2)

R. M. Lees, L.-H. Xu, B. E. Billinghurst, and D. R. T. Appadoo, “Weeding the cosmos--FIR synchrotron spectroscopy of methanol at the Canadian Light Source,” J. Mol. Structr. 993, 269-276 (2011).
[CrossRef]

H. S. P. Müller, F. Schlöder, J. Stutzki, and G. Winnewisser, “The Cologne database for molecular spectroscopy, CDMS: a useful tool for astronomers and spectroscopists,” J. Mol. Structr. 742, 215-227 (2005).
[CrossRef]

J. Nanoelectron. Optoelectron. (1)

H.-W. Hübers, S. G. Pavlov, H. Richter, A. D. Semenov, L. Mahler, A. Tredicucci, H. E. Beere, and D. A. Ritchie, “Molecular spectroscopy with terahertz quantum cascade lasers,” J. Nanoelectron. Optoelectron. 2, 101-107 (2007).
[CrossRef]

Mon. Not. R. Astron. Soc. (1)

D. M. Cragg, A. M. Sobolev, and P. D. Godfrey, “Models of class II methanol masers based on improved molecular data,” Mon. Not. R. Astron. Soc. 360, 533-545 (2005).
[CrossRef]

Nature (1)

W. Batrla, H. E. Matthews, K. M. Menten, and C. M. Walmsley, “Detection of strong methanol masers towards galactic H II regions,” Nature 326, 49-51 (1987).
[CrossRef]

Rev. Sci. Instrum. (1)

B. J. Drouin, F. W. Maiwald, and J. C. Pearson, “Application of cascaded frequency multiplication to molecular spectroscopy,” Rev. Sci. Instrum. 76, 093113 (2005).
[CrossRef]

Other (3)

J. C. Pearson, B. J. Drouin, A. Maestrini, I. Mehdi, J. Ward, R. H. Lin, S. Yu, J. J. Gill, B. Thomas, C. Lee, G. Chattopadhyay, E. Schlecht, F. W. Maiwald, P. F. Goldsmith, and P. Siegel, “Demonstration of a room temperature 2.48-2.75 THz coherent spectroscopy source,” Rev. Sci. Instrum. (to be published).
[CrossRef]

Submillimeter Analysis Program (SMAP), part of the CALPGM suite of spectral analysis programs available at http://spec.jpl.nasa.gov.

G. Moruzzi, B. P. Winnewisser, M. Winnewisser, I. Mukhopadhyay, and F. Struma, Microwave, Infrared and Laser Transitions of Methanol, Atlas of Assigned Lines from 0 to 1258 cm−1 (CRC Press, 1995).
[PubMed]

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Figures (39)

Fig. 1
Fig. 1

Energy levels ( J = K with asymmetry averaged) of the A-states in v t = 0 , 1, 2, and 3 in methanol. It is noted that the lowest small amplitude vibrational mode, the CO stretch (not shown), starts to overlap the third excited torsional state. Close inspection reveals several interactions, including the ground state K = 9 with v t = 1 K = 5 , v t = 1 K = 8 with 9, and ground state K = 15 with v t = 1 K = 13 and v t = 2 K = 11 . In these cases, the different torsional state levels have nearly the same energy. The cusp between v t = 2 and v t = 3 at K = 13 is also obvious.

Fig. 2
Fig. 2

Energy levels ( J = | K | ) of E-states in v t = 0 , 1, 2, and 3 in methanol. Once again, the CO stretch mode (not shown) begins to overlap the v t = 3 state, in particular the K = 5 level of v t = 3 in nearly degenerate and strongly mixed with the CO stretch E-state K = 5 level. A number of resonances can also be observed in this diagram by looking for levels with the same energy in different torsional states.

Fig. 3
Fig. 3

Rotation free torsional contributions to the energy of the A-states as a function of K. Note that v t = 2 and v t = 3 are nearly free rotors as can be observed in the nearly sawtooth progression of energy. The ground state is 127 cm 1 above the bottom of the 373 cm 1 barrier, making the top of the potential barrier 246 cm 1 on this plot.

Fig. 4
Fig. 4

Rotation free torsional contributions to the energy of the E-states as a function of K. Once again v t = 2 and v t = 3 are nearly free rotors, as can be observed in the nearly linear progression of energy in these states. The ground state is 127 cm 1 above the bottom of the 373 cm 1 potential barrier making the top of the barrier 246 cm 1 on this plot.

Fig. 5
Fig. 5

Composite tone burst modulated spectrum of methanol from 2.49 to 2.72 THz from the present study as seen by the bolometer through the experimental apparatus. The apparent signal strength varies due to changing source power, cell transmission, residual water vapor absorption, and detector response. The tone burst modulated data were collected with a 30 ms time constant in 200 kHz steps. Purging was utilized in the air paths between the source and cell and cell and detector, but some residual atmospheric pressure water remained.

Fig. 6
Fig. 6

Comparison of laser sideband (middle higher noise second derivative), the present submillimeter (bottom lower noise in second derivative), and the FTIR spectra (top in transmission) [6]. The laser sideband data were recorded using the 2522782 MHz methanol laser combined with a 2 9 GHz microwave synthesizer in a planar waveguide mixer. The methanol pressure was 50 m Torr . FTIR data were recorded with a Bruker IFS-120 with 2 γ ILS = 0.001 cm 1 in 2.7 m path at a pressure 112 m Torr [6]. Submillimeter data were recorded at 10 m Torr in a 2.3 m path with a 30 ms time constant and a 200 kHz step size. The same cell and detector were used for the laser sideband and submillimeter experiments.

Fig. 7
Fig. 7

Comparison of a QCL spectrum of methanol (blue online) [11] with the present work (red online). Power variations for the QCL and multiplier are shown above the second derivative spectrum. The QCL power spectrum shows the transmission of the line, while the multiplier power spectrum was done with an empty cell. The QCL spectrum is intentionally pressure broadened resulting in the wider line. The asymmetry of the QCL spectrum tracks the power variation across the line from the current ramp used in tuning. The frequency of the QCL was derived by locking it to a free-running methanol laser on the 2522782 MHz laser line.

Fig. 8
Fig. 8

A-state connectivity diagram where squares indicate levels determined by infrared combination differences [6], parallelograms indicate more recent infrared energy levels [10], and circles indicate levels with no infrared data. Thin black line connections are with microwave accuracy transition included in the analysis [7]. Light dashed (purple) line connections are microwave accuracy transitions included in the analysis [9] of v t = 3 . Light dotted (green) connections are microwave accuracy assignments not included in the RAM analysis. Thick black lines are new microwave accuracy connections from this work. It is noted that K = 14 of v t = 0 is listed as identified in the methanol atlas [6]. However, the single transition used as the basis for the identification comes from a TuFIR study [13] where a line at 1581394.716 MHz assigned to the correct assignment of this line is v t = 1 20 7 19 6 .

Fig. 9
Fig. 9

E-state connectivity diagram utilizing the same symbols as Fig. 8. K = 0 is repeated in both the + K and K levels to show the connections. Not shown are the numerous additional transitions allowed by mixing of the lowest K levels in the ground state.

Fig. 10
Fig. 10

Absorption spectrum of the 16 8 15 7 E line of the ground torsional state of the excited CO stretch vibration ( v co = 1 ) at 2522782.759(100). This transition is the well-known methanol laser line observed at 2522782.4 MHz [6]. The other two lines remain unidentified. A methanol laser utilizing this line was used as the laser in the laser sideband spectrum and was the source of stabilization for the QCL spectrum shown in Fig. 7.

Fig. 11
Fig. 11

Reduced energy level diagram of resonance between the A-state v t = 1 K = 5 and v t = 0 K = 9 . All energy J values have the J 0 + energy subtracted. No interaction with the v t = 2 K = 0 A-state level also shown on the diagram has been identified. The quantum levels were assigned on energy ordering, making this an avoided crossing. The intensities suggest that above J = 30 v t = 1 K = 5 should be the lower energy levels of the pair.

Fig. 12
Fig. 12

Allowed and interaction allowed transitions due to the resonance between the A-state v t = 1 K = 5 and v t = 0 K = 9 . The strong allowed b-type rotational transitions connect levels with Δ v t = 0 and 2, Δ K = + / 1 and are shown in solid (black). The strong allowed c-type torsional transitions Δ K = + / 1 , Δ v t = 1 are shown with solid (black) lines. The only strong a-type transitions are within each K substate and are not shown. The dotted (blue) lines indicate the transitions that are allowed through the mixing of the states.

Fig. 13
Fig. 13

Reduced energy level diagram of the A-state v t = 1 K = 8 and 9. Reduced energy is relative to J 0 + . Also shown is the close proximity to the A-state v t = 2 K = 1 , although no interaction with this state was identified. K = 8 and K = 9 of v t = 1 are strongly mixed by the internal rotation as manifested by the D a b ( P a P b + P b P a ) term in the RAM Hamiltonian.

Fig. 14
Fig. 14

The allowed solid (black) and interaction facilitated dotted (blue) transitions for the A-state v t = 1 K = 8 and 9 levels. In the RAM Hamiltonian, the levels are mixed by the D a b ( P a P b + P b P a ) term in the on diagonal in torsion part of the Hamiltonian. As a result, a number of extra bands are observed, including the TuFIR observation of the a-type R branch between v t = 0 and v t = 1 at K = 9 and the v t = 1 K = 10 to K = 9 and K = 10 to K = 8 Q branches observed in this work. The a-type R branch between v t = 0 and v t = 1 at K = 9 obtains its intensity from c-dipole torsional moment through the mixing of these levels.

Fig. 15
Fig. 15

Reduced energy levels of the A-state v t = 1 K = 4 and 6 levels relative to the ground A-state J 0 + levels. These two levels are strongly mixed by the asymmetry operators B P b 2 C P c 2 in the rotational Hamiltonian. This operator causes the levels to repel each other and explains their divergence with increasing J values.

Fig. 16
Fig. 16

The allowed solid (black) and allowed by mixing dotted (blue) transitions involving v t = 1 K = 4 and K = 6 A-state levels that are mixed by the asymmetry in the rotational part of the Hamiltonian. The result is extra bands with Δ K = 3 between K = 6 of v t = 1 and K = 3 of v t = 0 , 1, and 2 and between K = 4 of v t = 1 with K = 7 of v t = 0 , 1, and 2.

Fig. 17
Fig. 17

Reduced energy levels as assigned by the most recent RAM analysis [7] for the A-state v t = 0 K = 15 , v t = 1 K = 13 and v t = 2 K = 11 relative to the ground J 0 + levels. Energy ordering suggests the lowest of the three should be v t = 2 K = 11 , the level in the middle is v t = 0 K = 15 , and the highest energy level should be v t = 1 K = 13 . Above J = 24 the v t = 0 and v t = 1 levels are assigned the same energy and the third level of the system is omitted. These levels are strongly mixed by the P α , F p α 2 , and V ( α ) terms in the torsional part of the Hamiltonian. The ordering was recently confirmed with infrared data [10].

Fig. 18
Fig. 18

Allowed solid (black) and interaction facilitated dotted (blue) bands associated with the A-state v t = 2 K = 11 , v t = 1 K = 13 and v t = 0 K = 15 resonance. The normally allowed bands Δ v t = 0 , 1 Δ K = 1 are shown in black, while bands allowed by mixing are shown with dotted lines. Assignments were made by sorting the energy levels shown in Fig. 17 and interpolating where missing levels are observed. Agreement with the recent infrared study within quoted experimental errors [10].

Fig. 19
Fig. 19

Reduced energy level diagram of the A-state v t = 2 K = 13 and v t = 3 K = 13 relative to v t = 2 K = 13 . Zero energy for this plot was the v t = 2 K = 13 energy levels and the difference between v t = 2 and v t = 3 is shown on the plot. The energy levels were derived from the recent infrared study [10].

Fig. 20
Fig. 20

Allowed transitions solid (black) and facilitated dotted (blue) by the interaction of the A-state v t = 2 and v t = 3 at K = 13 . In this case, the resonance mixes the torsional wave functions, making each level contain a significant amount of two different free-rotor states allowing significant torsional overlaps with more states.

Fig. 21
Fig. 21

Reduced energy level diagram of the ground E-states with | K | < 5 relative to the ground E-state K = 0 . The reduced energy for all E-states was derived relative to the v t = 0 K = 0 E-state. Once again, energy ordering has been used so that the one crossing is avoided.

Fig. 22
Fig. 22

The resonance (double-ended arrows), allowed solid (black), and mixing facilitated dotted (blue) transitions in the ground E-state at low K due to the D a b ( P a P b + P b P a ) and B P b 2 C P c 2 terms in the RAM Hamiltonian. Successful analysis of the ground state of methanol required that these interactions be well characterized. Numerous additional transitions allowed by these mixings have been observed in the spectrum.

Fig. 23
Fig. 23

Reduced energy level diagram of v t = 1 K = 9 and 10 and K = 10 and 11 E-states relative to the ground E-state K = 0 . These two pairs of levels interact strongly through the D a b ( P a P b + P b P a ) term in the rotational part of the RAM Hamiltonian. The nature of the interaction is similar to the A-state v t = 1 K = 8 and 9 interaction.

Fig. 24
Fig. 24

The allowed solid (black) and facilitated by the interaction dotted (blue) transitions associated with the mixing of the E-state v t = 1 K = 9 and 10 . Several of the bands allowed by the mixing are observed in the spectrum.

Fig. 25
Fig. 25

The allowed solid (black) and facilitated by the interaction dotted (blue) transitions associated with the mixing of the E-state v t = 1 K = 10 and 11. Several of the bands allowed by the mixing are observed in the spectrum.

Fig. 26
Fig. 26

Reduced energy level diagram of v t = 1 K = 5 and 7 and K = 3 and 5 E-states relative to the ground E-state K = 0 . These two pairs of levels interact through the B P b 2 C P c 2 asymmetry parameter in the rotational part of the Hamiltonian. The interactions are similar to the A-state v t = 1 K = 4 and 6 interaction.

Fig. 27
Fig. 27

The allowed solid (black) the extra dotted (blue) transitions associated with v t = 1 K = 5 and 7 and their mixing. Several of the extra bands were observed in the spectrum.

Fig. 28
Fig. 28

The allowed solid (black) and extra dotted (blue) transitions associated with v t = 1 K = 3 and 5 and their mixing. Several of the extra bands were observed in the spectrum.

Fig. 29
Fig. 29

Reduced energy diagram of the E-state v t = 1 K = 6 , 7, and 8 relative to the ground E-state K = 0 . K = 6 and 8 interact through the B P b 2 C P c 2 part of the Hamiltonian, while K = 7 interacts with both K = 6 and 8 through the D a b ( P a P b + P b P a ) term. This complex mixing results in a dramatic departure from standard asymmetric-top intensities in transitions between these levels.

Fig. 30
Fig. 30

Allowed solid (black) and interaction facilitated dotted (blue) transitions from E-state v t = 1 K = 6 , 7, and 8. The closest analog in the spectrum to this series of interactions is the low K ground state interactions shown in Figs. 21, 22.

Fig. 31
Fig. 31

Reduced energy level diagram for the E-state v t = 2 and 3 K = 8 relative to v t = 2 K = 8 . Energy levels were taken from the methanol atlas [6] and are shown relative to v t = 2 K = 8 . Like the A-state v t = 2 and v t = 3 K = 13 case, the mixing is between the free-rotor states, making each level effectively a combination of two different basis functions.

Fig. 32
Fig. 32

The allowed solid (black) and allowed dotted (blue) by mixing transition involving v t = 2 and 3 K = 8 . In this case, the levels are in the free-rotor limit so that torsional overlaps dominate the intensities of transitions.

Fig. 33
Fig. 33

Reduced energy level diagram of the triplet of states involving the E-state v t = 2 K = 10 , v t = 1 K = 12 and v t = 0 K = 14 relative to the ground E-state K = 0 . Calculated energies are shown as assigned by the level labeling scheme. A strict energy ordering like for the A-state v t = 0 K = 15 , v t = 1 K = 13 and v t = 2 K = 11 appears to make more sense from the perspective of intensities.

Fig. 34
Fig. 34

The allowed solid (black) and facilitated by the interaction dotted (blue) transitions associated with the mixing of the E-state v t = 2 K = 10 , v t = 1 K = 12 , and v t = 0 K = 14 .

Fig. 35
Fig. 35

Reduced energy level diagram for the quartet of states involving the E-state v t = 2 K = 10 and 12 , v t = 1 K = 14 , and v t = 0 K = 16 relative to the ground E-state K = 0 . The determined level labels are shown as calculated. Energy ordering suggest that v t = 1 K = 14 is the lowest level, v t = 2 K = 10 is next, v t = 2 K = 12 , and then v t = 0 K = 16 is the highest level.

Fig. 36
Fig. 36

The allowed solid (black) and facilitated by the interaction dotted (blue) transition associated with the E-state v t = 2 K = 10 and 12 , v t = 1 K = 14 , and v t = 0 K = 16 .

Fig. 37
Fig. 37

Reduced energy level diagram for the two triplets of states involving the E-state v t = 2 K = | 13 | , v t = 1 K = | 15 | , and v t = 0 K = | 17 | . There is no interaction between + K and K . These interactions are similar to the two previous E-state triplets and the A-state v t = 0 K = 15 , v t = 1 K = 13 , and v t = 2 K = 11 interaction. In both of these cases, the labeling of levels was not scrambled.

Fig. 38
Fig. 38

The allowed solid (black) and interaction allowed dotted (blue) transitions associated with the E-state v t = 2 K = 13 , v t = 1 K = 15 , and v t = 0 K = 17 .

Fig. 39
Fig. 39

The allowed solid (black) and interaction allowed dotted (blue) transitions associated with the E-state v t = 2 K = 13 , v t = 1 K = 15 , and v t = 0 K = 17 .

Tables (15)

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Table 1 Comparison of TuFIR Frequencies with This Work a

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Table 2 Comparison of Laser Sideband with the Present Work

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Table 3 v t = 0 A-States Measured during This Work

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Table 4 v t = 1 A-State Transitions Measured during This Work

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Table 5 v t = 2 A-State Transitions Measured during This Work

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Table 6 v t = 1 to v t = 0 A-State Transitions Measured during This Work

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Table 7 v t = 2 to v t = 1 A-State Transitions Measured during This Work

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Table 8 v t = 3 to v t = 2 and v t = 3 A-State Transitions Measured during This Work

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Table 9 v t = 0 E-State Transitions Measured during This Work

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Table 10 v t = 1 E-State Transitions Measured during This Work

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Table 11 v t = 2 E-State Transitions Measured during This Work

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Table 12 v t = 1 to v t = 0 E-State Transitions Measured during This Work

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Table 13 v t = 2 to v t = 1 E-State Transitions Measured during This Work

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Table 14 v t = 3 to v t = 2 E-State Transitions Measured during This Work

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Table 15 Determined K Subband Origins in v t = 2 Relative to Calculated Origin

Equations (5)

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H = ( p ρ a P a ) F ( p ρ a P a ) ρ b P b F ( p ρ a P a ) ( p ρ a P a ) F ρ b P b + ρ b 2 F P b 2 + P T μ P + V ,
H = A P a 2 + B P b 2 + C P c 2 + ( p α ρ a P a ) F ( p α ρ a P a ) + D a b ( P a P b + P b P a ) 2 p α F ρ b P b + 1 2 V 3 ( 1 cos 3 α ) + 1 2 V 6 ( 1 cos 6 α ) + . ,
H RAM = H T + H R + H c d + H int ,
H T = F ( p α ρ P a ) 2 + V ( α ) ,
H R = A RAM P a 2 + B RAM P b 2 + C RAM P c 2 + D a b ( P a P b + P b P a ) ,

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