Abstract

A “pressure modulator” has been constructed for use in studies of modulated infrared emission and absorption spectra. The modulator provides sinusoidal variation of the volume of a gas sample at a frequency of 8 cps with compression ratios of 2:1, 3:1, 4:1, 5:1, and 6:1. The general results obtained in grating studies of the fundamental and first-overtone absorption bands of carbon monoxide can be satisfactorily interpreted on the basis of an adiabatic modulation cycle, although detailed checks of the expected behavior for transitions between high rotational states were not entirely successful. In the adiabatic modulation of a gas for which γ=1.66, temperatures as high as 640°K and as low as 225°K are attained in the present modulator with a compression ratio of 5:1 without raising the cell temperature more than 45 K deg above room temperature.

© 1961 Optical Society of America

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References

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  1. In this expression A(ν) represents the fraction of incident radiation of frequency ν absorbed by the sample; A(ν) will be referred to as the absorption at frequency ν.
  2. J. N. Howard, D. E. Burch, and D. Williams, J. Opt. Soc. Am. 46, 186, 237, 242, 334, 452 (1956) (bibliography of early studies).
    [CrossRef]
  3. J. C. Gilfert and D. Williams, J. Opt. Soc. Am. 48, 765 (1958); J. Opt. Soc. Am. 49, 212 (1959).
    [CrossRef]
  4. From the Bellofram Corporation, Burlington, Massachusetts.
  5. J. R. Nielsen, V. Thornton, and E. B. Dale, Revs. Modern Phys. 16, 307 (1944).
    [CrossRef]
  6. R. Ladenberg and F. Reiche, Ann. Physik 42, 181 (1913).
    [CrossRef]
  7. W. M. Elsasser, Harvard Meteorological Studies No. 6, Harvard University, Cambridge, Massachusetts (1942).
  8. S. S. Penner and D. Weber, J. Chem. Phys. 19, 807 (1951); J. Chem. Phys. 19, 817 (1951).
    [CrossRef]
  9. J. H. Shaw and W. L. France, , Air Force Cambridge Research Center contract, and Ohio State University Research Foundation.
  10. E. B. Singleton, Doctoral dissertation, The Ohio State University, Columbus, Ohio (1958).

1958 (1)

1956 (1)

1951 (1)

S. S. Penner and D. Weber, J. Chem. Phys. 19, 807 (1951); J. Chem. Phys. 19, 817 (1951).
[CrossRef]

1944 (1)

J. R. Nielsen, V. Thornton, and E. B. Dale, Revs. Modern Phys. 16, 307 (1944).
[CrossRef]

1913 (1)

R. Ladenberg and F. Reiche, Ann. Physik 42, 181 (1913).
[CrossRef]

Burch, D. E.

Dale, E. B.

J. R. Nielsen, V. Thornton, and E. B. Dale, Revs. Modern Phys. 16, 307 (1944).
[CrossRef]

Elsasser, W. M.

W. M. Elsasser, Harvard Meteorological Studies No. 6, Harvard University, Cambridge, Massachusetts (1942).

France, W. L.

J. H. Shaw and W. L. France, , Air Force Cambridge Research Center contract, and Ohio State University Research Foundation.

Gilfert, J. C.

Howard, J. N.

Ladenberg, R.

R. Ladenberg and F. Reiche, Ann. Physik 42, 181 (1913).
[CrossRef]

Nielsen, J. R.

J. R. Nielsen, V. Thornton, and E. B. Dale, Revs. Modern Phys. 16, 307 (1944).
[CrossRef]

Penner, S. S.

S. S. Penner and D. Weber, J. Chem. Phys. 19, 807 (1951); J. Chem. Phys. 19, 817 (1951).
[CrossRef]

Reiche, F.

R. Ladenberg and F. Reiche, Ann. Physik 42, 181 (1913).
[CrossRef]

Shaw, J. H.

J. H. Shaw and W. L. France, , Air Force Cambridge Research Center contract, and Ohio State University Research Foundation.

Singleton, E. B.

E. B. Singleton, Doctoral dissertation, The Ohio State University, Columbus, Ohio (1958).

Thornton, V.

J. R. Nielsen, V. Thornton, and E. B. Dale, Revs. Modern Phys. 16, 307 (1944).
[CrossRef]

Weber, D.

S. S. Penner and D. Weber, J. Chem. Phys. 19, 807 (1951); J. Chem. Phys. 19, 817 (1951).
[CrossRef]

Williams, D.

Ann. Physik (1)

R. Ladenberg and F. Reiche, Ann. Physik 42, 181 (1913).
[CrossRef]

J. Chem. Phys. (1)

S. S. Penner and D. Weber, J. Chem. Phys. 19, 807 (1951); J. Chem. Phys. 19, 817 (1951).
[CrossRef]

J. Opt. Soc. Am. (2)

Revs. Modern Phys. (1)

J. R. Nielsen, V. Thornton, and E. B. Dale, Revs. Modern Phys. 16, 307 (1944).
[CrossRef]

Other (5)

From the Bellofram Corporation, Burlington, Massachusetts.

W. M. Elsasser, Harvard Meteorological Studies No. 6, Harvard University, Cambridge, Massachusetts (1942).

J. H. Shaw and W. L. France, , Air Force Cambridge Research Center contract, and Ohio State University Research Foundation.

E. B. Singleton, Doctoral dissertation, The Ohio State University, Columbus, Ohio (1958).

In this expression A(ν) represents the fraction of incident radiation of frequency ν absorbed by the sample; A(ν) will be referred to as the absorption at frequency ν.

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Figures (6)

Fig. 1
Fig. 1

Apparatus for modulation of the pressure.

Fig. 2
Fig. 2

Comparison of conventional and pressure-modulated tracings of the R branch of the 2143 cm−1 carbon monoxide band. The gains used in obtaining the two lower spectra were slightly higher than that used in obtaining the conventional spectrum but were equal. Frequencies increase toward the left in the tracings; the numbers on the lines are J values of the upper rotational states involved.

Fig. 3
Fig. 3

Variation of temperature, absorber concentration w, and pressure P over a cycle. All amplitudes have been normalized for comparison.

Fig. 4
Fig. 4

Dependence of the total absorptions of lines in the 4260 cm−1 CO band on J value for various compression ratios.

Fig. 5
Fig. 5

Spectra of the R branch of the 2143 cm−1 CO band showing the dependence of total absorption of individual lines on temperature for a constant compression ratio. w=0.81 atm-cm.

Fig. 6
Fig. 6

Plots of the calculated total absorptions for weak lines of CO vs 2π ft for three lines. The amplitudes have been normalized to the same value for comparison of the shapes. (SJwNJ′/V). The uppermost curve is that for J=1; the lowest curve is that for J=20.

Tables (1)

Tables Icon

Table I Temperature ranges for various compression ratios and ratios of specific heats.

Equations (2)

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A ( ν ) d ν = [ 2 S V α 0 ( T 0 / P 0 ) P 2 / T 2 w V / V 2 ( T 2 / T 0 ) ] 1 2 × [ ( N J ) 2 1 2 - ( T 1 / T 2 ) 1 4 1 / C ( N J ) 1 1 2 ] ,
N J = h c B / k T ( J + J + 1 ) exp [ - h c B J ( J + 1 ) / k T ] ,