Open Access
Add to BibSonomy
Abstract
Dimerization reactions play a critical role in various fields of research, including cell biology, biomedicine, and chemistry. In particular, the dimerization reaction of 2NO2$\rightleftharpoons$N2O4 has been extensively applied in pollution control and raw material preparation. Spectroscopy, as a powerful tool for investigating molecular structures and reaction kinetics, has been increasingly employed to study dimerization reactions in recent years. In this study, we successfully demonstrated the application of dual-comb spectroscopy (DCS) to analyze NO2 dimerization reactions, making the first report on the application of this technique in this context. Parallel measurements of NO2 and N2O4 fingerprints spectra with high resolution at 3000 cm-1 was performed, benefiting from the unprecedented broadband and high-precision capability of DCS. The absorption cross-sections of N2O4 from 296 to 343 K was obtained from the measured spectra, which contributes to further research on the molecular spectrum of N2O4. These results demonstrate the potential of DCS for studying the dimerization reaction mechanism.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Dimerization is a common process in nature and industrial production [1–3], which serves as a means of synthesizing complex molecules, materials, and drugs [4–7]. With the advancement of industrialization and accumulation of environmental problems, nitrogen oxides (NOx) have attracted significant attention in recent years. Nitrogen dioxide (NO2), a major air pollutant, plays a significant role in the formation of photochemical smog and acid rain, as well as in the destruction of stratospheric ozone. It also serves as a value-added multifunctional reagent in organic synthesis and chemical production, acting as both a nitrite catalyst and raw material for nitric acid [8]. Meanwhile, its dimer-nitrogen tetroxide (N2O4), as a raw material for ultra-low freezing point oxidants, is the key to achieving rocket propellants with excellent performance and contributes to the development of the space industry [9]. However, the presence of unpaired electrons induces a dimerization reaction, resulting in the coexistence of NO2 and N2O4 in the atmosphere [10]. This poses a challenge for gas extraction, making it difficult to analyze individual gases. Therefore, the parallel measurement of the monomers and dimers of the dimerization reaction is urgently needed, which is of great significance for studying the mechanism and parameters of the reaction in a complex gas environment.
Extensive studies have been conducted on NOx. Among the various techniques [11–16], spectroscopy has gained widespread popularity owing to its unique advantages of non-invasive detection, rapid response time, and simple experimental systems. These include Fourier transform infrared spectroscopy (FTIR), non-dispersive infrared technique (NDIR), differential Absorption Lidar (DIAL), and cavity ring-down technology (CRD). The FTIR technique enables the parallel measurement of multiple gases with broadband spectral coverage. However, its resolution limitations render it unsuitable for low-pressure conditions [17]. Although NDIR technique is cost-effective, it has a lower resolution than FTIR and requires pre-calibration [18]. The DIAL technique offers greater operational convenience than NDIR technique, enabling long-range and high-precision detection of specific gases [19,20]. In addition, the CRD technique requires coated high-reflection mirrors to achieve long optical path and high-sensitivity gas measurements [21]. In summary, the limitations of the spectral width, spectral resolution, and system stability make it challenging for these techniques to simultaneously investigate both the reactants and products of chemical reactions in complex environments.
Dual-comb spectroscopy (DCS) is a powerful measurement technique that offers several advantages over other methods, including the ability to maintain broadband, high-precision, and high-resolution within a short acquisition time. This technique has demonstrated extensive potential in applications such as distance measurement, atmospheric monitoring, and the investigation of dynamic processes [22–25]. Using this technique, Muraviev et al. achieved parallel detection of multiple trace molecular species in gas mixtures [26]. Furthermore, as an efficient and accurate measurement tool, DCS has achieved a series of achievements in kinetic research. Research on multiple chemical reactions has been conducted, including the exploration of reaction rate and mechanism [27,28]. Yun et al. successfully measured several flow parameters of a high-speed combustor to study combustion kinetics [29]. DCS has been applied in various frontier kinetic studies. However, there are still certain gaps that need to be addressed in the field of kinetic research, such as the investigation of dimerization reactions.
In this letter, we investigated monomeric and dimer in 2NO2$\rightleftharpoons$2O4 dimerization reaction under different temperature based on the mid-infrared (MIR) dual-comb spectroscopy. To the best of our knowledge, it is the first demonstration that the parallel measurement of the ν1+ν3 vibrational band of NO2 and the ν1+ν9 vibrational band of N2O4 at 3000 cm-1. The absorption spectra of monomeric NO2 and dimeric N2O4 were measured from 298 to 343 K and showed good agreement with the theoretical results from the HITRAN database. In the experiment, the concentrations of NO2 were precisely obtained from the measured spectra. However, due to the lack of the absorption cross-sections, the concentrations of N2O4 under different temperatures was obtained based on theoretical equilibrium constants of 2NO2$\rightleftharpoons$N2O4 dimerization reaction. Then, the absorption cross-sections of N2O4 at different temperatures was built based on the measured high-resolution spectra of N2O4, which contributed to the improvement of the absorption molecular database and promoted further research on N2O4 in complex gas environments. These results demonstrate the potential of dual-comb spectroscopy as a powerful tool for researching polymerization, chemical reaction processes, and kinetics.
2. Experimental methods
Dimerization in the gas-phase is a chemical equilibrium process in which two molecules combine to form a single molecule (dimer), accompanied by characteristic changes in the absorption spectral frequency. DCS with broadband, high resolution and high sensitivity is of great significance in the measurement of frequency variation and the high precision measurement of spectra, and the basic principle of the dimerization reaction (2NO2$\rightleftharpoons$N2O4) detection system based on dual-comb spectroscopy is shown in Fig. 1(a). The two highly coherent mid-infrared frequency combs used in our experiment have been reported in previous studies [30–32], in which a mid-infrared CW laser at 2964 cm-1 (Nanoplus, NP-ICL-3370-TO66-HC) served as the frequency standard. In the frequency domain aspect, the two combs passively inherit same CW frequency but with slightly different repetition rates of ∼108.4 MHz (the repetition frequency difference was set to 600 Hz). To avoid frequency aliasing, an optical filter was used to isolate the frequency components aside the CW frequency tooth. Additionally, for the measurement of NO2 and N2O4, the absorption spectra were perfectly divided by an optical filter. The configuration of the dimerization reaction is shown in Fig. 1(b). The optical frequency combs with a coverage range of 2830-3160 cm-1 are spatially combined on a pellicle beam-splitter and then pass through a heated gas cell (the heating furnace were provided by Hefei Kejing, OTF-1200X-S-II, with a temperature control accuracy of ±1 K, and an optical length of 11.5 cm). The output was split into two branches using a beam splitter and then spectral filtered to achieve heterodyne detection of the spectral components aside the CW frequency. Two mid-infrared balanced detectors were used to improve the spectral signal-to-noise ratio. The recorded electrical signal was subsequently fed into two different channels of a 12-bit analog-to-digital acquisition card (ATS9350; AlazarTech,). Thus, the spectra of NO2 and N2O4 were measured simultaneously, ingeniously avoiding frequency aliasing and optimizing the spectral signal-to-noise ratio.
Fig. 1. Schematic and experimental layout for the dimerization reaction of 2NO2$\rightleftharpoons$N2O4 based on DCS. (a) Parallel measurements of NO2 and N2O4 absorption spectra based on DCS. (b) Diagram of the experimental setup. BD, balanced detector; BS, beam splitter.
3. Results and discussion
3.1 Performance of DCS
To evaluate the performance of MIR DCS for the characterization of dimerization reactions, tooth-resolved comb spectra were investigated. Figure 2 displays the original detector signals of channel A (left) and channel B (right) captured with the evacuated gas cell, which were used to detect the information of NO2 and N2O4, respectively. The 200-s data streams from Channel A and Channel B were divided into 200 parts to perform averaging and Fourier transformation. To facilitate the subsequent analysis, the spectral signals measured by the two channels were normalized. Channel A recorded spectra covered from 2830 to 2930 cm-1, and channel B recorded spectral coverage from 2980 to 3160 cm-1, as shown in Fig. 2(a). The spectral gap was caused by the spectral filters. Figure 2(b) and 2(c) show the tooth-resolved spectra of the different channels, which enable high-resolution spectra acquisition. The peak signal-to-noise ratio (SNR) is around 500 at about 2904 cm-1. Figure 2(d) and (e) show magnified views of the tooth-resolved spectrum, demonstrating the broadband spectral comb-resolved properties. The spectral resolution (frequency interval of comb teeth) is 108.4 MHz and the linewidth of the heterodyne comb teeth is 1 Hz in the RF domain (190 kHz in the optical domain), limited by the FFT time. These measurement results demonstrate the high mutual coherence of broadband DCS, which is essential for achieving high-precision parallel measurements of both monomeric NO2 and dimer N2O4.
Fig. 2. Tooth-resolved dual-comb spectra. (a) Broadband spectrum obtained by DCS. (b),(c) The tooth-resolved spectra of different channel with a measurement time of 200 s. (d),(e) Zoomed figure display comb-tooth-resolved spectra with a repetition rate of 108.4 MHz.
3.2 Measurement of NO2 spectrum
To verify the high-precision molecular spectrum measurement capability of DCS, we recorded the absorption spectra of NO2 and N2O4 over the temperature range from 296 to 343 K, simultaneously. It is crucial to achieve precise analysis of the dimerization reactions. Firstly, we heated and stabilized the gas cell to a set temperature. The gas cell was purged with N2 prior in order to prevent interference from impurity gases in the atmosphere. Then the NO2 gas with concentration of 99.5% (0.5% impurity gases) was filled into the gas cell. After the dimerization reaction reached equilibrium, the absorption spectra of the reactant and product were recorded at a pressure of 100 mbar and set temperature. To achieve the spectrum measurements at a fixed pressure under different temperatures, we adjusted the set temperature, and repeated the steps. The absorption spectra of the reactant and product were recorded at different temperatures after reaching equilibrium state. Figure 3 shows the absorption spectrum of NO2. In order to achieve a higher sensitivity for the detection of NO2 molecules, we used a spectral filtering technique based on gratings and slits to narrow the spectra [33]. The NO2 spectra measured by DCS at 296 K with a high SNR is shown in Fig. 3(a), and the peak SNR is beyond 7200 with a measurement time of 200 s. The detection sensitivity of NO2 spectra obtained by DCS was 0.1%, which is defined as the relative (with respect to the mean value) standard deviation of the spectral power density in a given spectral region [26]. This is essential for investigating trace gases in chemical kinetic analysis. Figure 3(b) shows a comparison between the measured and theoretical absorption spectra, as well as the residual between them. The standard deviation of the residual is 1.07%, which results from some ignored narrowing effects in the simulations of the HITRAN database, such as Dicke narrowing and the speed dependence of the collisional mechanism [34,35]. The high-precision measurement of molecular spectra by DCS is beneficial for investigating the temperature dependence of the dimerization equilibrium reaction. The absorption spectra of NO2 were measured over a temperature range of 296-343 K, with a temperature interval of 10 K, as shown in Fig. 3(c). There was a significant change in the absorbance of the monomer and dimer at varying temperatures, which can be attributed to the temperature-dependent nature of the absorption cross-sections and concentration. The precise concentration of NO2 at different temperatures was obtained by combining the measured spectra with the theoretical spectra calculated based on the parameters from the HITRAN database. It can be seen that as temperature rises, NO2 concentrations continuously increases, indicating that the dimerization reaction of NO2$\rightleftharpoons$N2O4 shifts towards the direction of NO2 production. These results demonstrate the precise measurement capability of DCS for dimerization reactions.
Fig. 3. Absorption spectra of NO2 at different temperatures with a pressure of 100 mbar. (a) Measurement spectra of NO2 based on DCS at 296 K with a high SNR. (b) Comparison between the extracted absorption lines (blue line) and the theoretical absorption lines (red line) computed based on the HITRAN database of NO2 at 296 K, and the standardized residual is 1.07%. (c) The NO2 absorption lines were measured at 10 K intervals within the temperature range of 296-343 K. T, temperature; X: concentration of NO2.
3.3 Absorption cross-sections of N2O4
Spectroscopy is a powerful analytical technique that provides rich molecular information. However, the concentrations of N2O4 could not be directly determined from the measured spectra, mainly because of the lack of a corresponding absorption cross-sections. This can be attributed to the challenges of extracting N2O4 from the dimerization reaction, which limited the development of related researches. Some experiments measured the N2O4 spectra in the temperature range of 261-298 K and at a lower temperature of 100 K at 1261-1757cm-1 [17,36,37]. In the experiment, we achieved the analysis of N2O4 at 3000 cm-1 within the temperature range of 296-343 K based on the dynamic equilibrium relationship between the monomer and dimer. The concentrations of N2O4 at reaction equilibrium were determined using the equilibrium constants at different temperatures, while the NO2 concentrations were simultaneously measured from the measured spectra. The temperature dependence function of the equilibrium constants provided by NASA is expressed as follows:
where A = 5.9 × 10−29 cm3 molecule-1, and B = 6643 K [21,38]. For the 2NO2$\rightleftharpoons$N2O4 dimerization equilibrium reaction, the reaction equilibrium constant K is defined as, where XNO2 and XN2O4 are the concentrations of NO2 and N2O4, respectively. The practical concentrations of N2O4 at different temperatures were calculated using the given equilibrium constants and the exact concentrations of NO2. The measured concentrations of NO2 and N2O4 are shown in Fig. 4. The total concentrations of the two gases under the same experimental conditions were slightly lower than 1, which was influenced by the impurity gases. In this experiment, precise molecular concentrations were obtained by the simultaneous measurement of monomers and dimers, thereby avoiding the problem of impurities and providing a strong foundation for subsequent researches.N2O4 is bound by an N-N bond, and its bond energy is approximately 14 kcal/mol, which is significantly smaller than the N-O bond in NO2 (approximately 120 kcal/mol). The effective mass at both ends of the N-N bond is large, which leads to a reduction in the vibration and rotation energy level interval of N2O4. On the other hand, temperature-induced Doppler broadening and collisional broadening exacerbate the overlap of the spectral lines [39], rendering the rotational structure of N2O4 unresolved [38,40]. We realized the measurements of N2O4 absorbance at 3110 cm-1 using DCS during the dimerization reaction from 296 to 343 K, and the correlation between absorbance and temperature is shown in Fig. 5(a). It can be seen that the absorbance of N2O4 gradually decreased with an increase in temperature. According to the Beer-Lambert law, the absorbance is affected by the pressure, the optical path, the absorber mole fraction, and the temperature-dependent absorption cross-sections. However, the optical path length and total pressure remain constant in our work. Therefore, the change of absorbance was attributed to the temperature-dependent changes in concentration and absorption cross-sections.
Fig. 5. Measurement results of N2O4 molecules at different temperatures. (a) The absorbances of the N2O4 at different temperatures measured by DCS from 296 to 343 K. (b) The absorption cross-sections of the N2O4 under different temperatures. (c) The absorption cross-sections with temperatures at different wavenumber.
The absorbances αν of N2O4 conform to Beer–Lambert law:
where the pressure P [atm] was measured using a high-precision barometer, and the concentration X [dimensionless] as shown in Fig. 4. Subsequently, the absorption cross-sections σ(ν,T) [atm-1cm-1], which is a function of wavenumber and temperature, would be calculated using Eq. (3). In order to match the widely used HITRAN database, the measured cross-sections σ(ν,T) follows a transformation relation:The calculated results for different temperatures are shown in Fig. 5(b). The absorption cross-sections of N2O4 exhibited a positive correlation with temperature within the range of 296-343 K, which is inversely related to the trend observed in absorbance. It can be attributed to the combined influence of concentration and absorption cross-sections on absorbance. Therefore, while the absorption cross-sections increase with temperature within the range of 296-343 K, decreasing concentration results in a decrease in absorbance with increasing temperature. As shown in Fig. 5(c), the temperature-dependent absorption cross-sections exhibits consistency at different wavenumbers. The acquisition of cross-sections data provides a fundamental parameter for quantitative measurements of the N2O4 concentration, and contributes to the improvement of the absorption molecular database.
4. Conclusions
In conclusion, we successfully employed mid-infrared dual-comb spectroscopy for the first time to study dimerization reactions. Parallel measurement of the spectra of monomeric NO2 and dimer N2O4 in the reaction at 3000 cm-1 was realized. More importantly, the absorption cross-sections of N2O4 was obtained by further combining the known NO2 spectral parameters from HITRAN and the equilibrium constants, which can be used for the subsequent spectroscopic analysis of N2O4 in complex gas environments and to supplement the molecular database. The results demonstrate the potential of DCS technology to achieve the spectral measurements with high spectral resolution and broadband spectral coverage for analyzing dimerization reactions under different conditions in complex environments. In the future, we will extend our dual-comb spectroscopy to study chemical reaction processes and kinetics.
Funding
National Natural Science Foundation of China (12104162, 12134004, 12204178, 12274141).
Disclosures
The authors declare no conflicts of interest.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. K. E. Preuss, “Pancake bonds: π-Stacked dimers of organic and light-atom radicals,” Polyhedron 79, 1–15 (2014). [CrossRef]
2. Y. Scribano, N. Goldman, R. J. Saykally, and C. Leforestier, “Water Dimers in the Atmosphere III: Equilibrium Constant from a Flexible Potential,” J. Phys. Chem. A 110(16), 5411–5419 (2006). [CrossRef]
3. D. Teng, K. Wang, Z. Li, and Y. Zhao, “Graphene-coated nanowire dimers for deep subwavelength waveguiding in mid-infrared range,” Opt. Express 27(9), 12458 (2019). [CrossRef]
4. A. Paquin, C. Reyes-Moreno, and G. Bérubé, “Recent Advances in the Use of the Dimerization Strategy as a Means to Increase the Biological Potential of Natural or Synthetic Molecules,” Molecules 26(8), 2340 (2021). [CrossRef]
5. R. DeRose, T. Miyamoto, and T. Inoue, “Manipulating signaling at will: chemically-inducible dimerization (CID) techniques resolve problems in cell biology,” Pflugers Arch - Eur J Physiol 465(3), 409–417 (2013). [CrossRef]
6. D. T. Dang, “Molecular Approaches to Protein Dimerization: Opportunities for Supramolecular Chemistry,” Front. Chem. 10, 829312 (2022). [CrossRef]
7. C. Chen, M. R. Alalouni, P. Xiao, G. Li, T. Pan, J. Shen, Q. Cheng, and X. Dong, “Ni-Loaded 2D Zeolitic Imidazolate Framework as a Heterogeneous Catalyst with Highly Activity for Ethylene Dimerization,” Ind. Eng. Chem. Res. 61(38), 14374–14381 (2022). [CrossRef]
8. J. Li, X. Han, X. Zhang, A. M. Sheveleva, Y. Cheng, F. Tuna, E. J. L. McInnes, L. J. McCormick McPherson, S. J. Teat, L. L. Daemen, A. J. Ramirez-Cuesta, M. Schröder, and S. Yang, “Capture of nitrogen dioxide and conversion to nitric acid in a porous metal–organic framework,” Nat. Chem. 11(12), 1085–1090 (2019). [CrossRef]
9. M. Shiri, M. A. Zolfigol, H. G. Kruger, and Z. Tanbakouchian, “Advances in the application of N2O4/NO2 in organic reactions,” Tetrahedron 66(47), 9077–9106 (2010). [CrossRef]
10. A. Amoruso, L. Crescentini, G. Fiocco, and M. Volpe, “New measurements of the NO2 absorption cross section in the 440- to 460-nm region and estimates of the NO2-N2O4 equilibrium constant,” J. Geophys. Res. 98(D9), 16857 (1993). [CrossRef]
11. S. Thompho, S. Fritzsche, T. Chokbunpiam, T. Remsungnen, W. Janke, and S. Hannongbua, “Adsorption and the Chemical Reaction N2O4 ↔ 2NO2 in the Presence of N2 in a Gas Phase Connected with a Carbon Nanotube,” ACS Omega 6(27), 17342–17352 (2021). [CrossRef]
12. F. Ghasemi, “Vertically aligned carbon nanotubes, MoS2–rGo based optoelectronic hybrids for NO2 gas sensing,” Sci. Rep. 10(1), 11306 (2020). [CrossRef]
13. J. Chen, D.-N. Wang, A. Ramachandran, S. Chandran, M. Li, and R. Varma, “An open-path dual-beam laser spectrometer for path-integrated urban NO2 sensing,” Sens. Actuators, A 315, 112208 (2020). [CrossRef]
14. Z.-H. Yang, Y.-C. Yang, L.-Z. Deng, and J.-P. Yin, “Absolute density measurement of nitrogen dioxide with cavity-enhanced laser-induced fluorescence,” Chin. Phys. B 27(10), 100601 (2018). [CrossRef]
15. Y. Maeda, K. Aoki, and M. Munemori, “Chemiluminescence method for the determination of nitrogen dioxide,” Anal. Chem. 52(2), 307–311 (1980). [CrossRef]
16. R. K. Hanson, “Applications of quantitative laser sensors to kinetics, propulsion and practical energy systems,” Proc. Combust. Inst. 33(1), 1–40 (2011). [CrossRef]
17. D. Wilson, G. Duxbury, and N. Langford, “Fourier transform and multiplexed intrapulse quantum cascade laser spectrometer measurements of NO2 and its dimer N2O4,” Can. J. Phys. 91(11), 941–948 (2013). [CrossRef]
18. M. Xu, C. Gao, and Y. Guo, “Design of nitrogen oxide detection system based on non-dispersive infrared technology,” Optik 262, 169351 (2022). [CrossRef]
19. Y. Gong, L. Bu, B. Yang, and F. Mustafa, “High Repetition Rate Mid-Infrared Differential Absorption Lidar for Atmospheric Pollution Detection,” Sensors 20(8), 2211 (2020). [CrossRef]
20. L. Mei, P. Guan, and Z. Kong, “Remote sensing of atmospheric NO2 by employing the continuous-wave differential absorption lidar technique,” Opt. Express 25(20), A953 (2017). [CrossRef]
21. M. F. Tuchler, K. L. Schmidt, and M. Morgan, “A CRDS approach to gas phase equilibrium constants: the case of N2O4↔2NO2 at 283 K,” Chem. Phys. Lett. 401(4-6), 393–399 (2005). [CrossRef]
22. I. Coddington, N. Newbury, and W. Swann, “Dual-comb spectroscopy,” Optica 3(4), 414 (2016). [CrossRef]
23. G. Ycas, F. R. Giorgetta, K. C. Cossel, E. M. Waxman, E. Baumann, N. R. Newbury, and I. Coddington, “Mid-infrared dual-comb spectroscopy of volatile organic compounds across long open-air paths,” Optica 6(2), 165 (2019). [CrossRef]
24. A. M. Zolot, F. R. Giorgetta, E. Baumann, J. W. Nicholson, W. C. Swann, I. Coddington, and N. R. Newbury, “Direct-comb molecular spectroscopy with accurate, resolved comb teeth over 43 THz,” Opt. Lett. 37(4), 638 (2012). [CrossRef]
25. X. Zou, C. Gu, M. Zhang, Z. Zuo, D. Peng, Y. Di, L. Tang, Y. Liu, D. Luo, C. Zhou, S. Li, X. Xu, and W. Li, “208-µs single-shot multi-molecular sensing with spectrum-encoded dual-comb spectroscopy,” Opt. Express 29(17), 27600 (2021). [CrossRef]
26. A. V. Muraviev, V. O. Smolski, Z. E. Loparo, and K. L. Vodopyanov, “Massively parallel sensing of trace molecules and their isotopologues with broadband subharmonic mid-infrared frequency combs,” Nat. Photonics 12(4), 209–214 (2018). [CrossRef]
27. T. Q. Bui, B. J. Bjork, P. B. Changala, T. L. Nguyen, J. F. Stanton, M. Okumura, and J. Ye, “Direct measurements of DOCO isomers in the kinetics of OD + CO,” Sci. Adv. 4(1), eaao4777 (2018). [CrossRef]
28. P.-L. Luo and E.-C. Horng, “Simultaneous determination of transient free radicals and reaction kinetics by high-resolution time-resolved dual-comb spectroscopy,” Commun. Chem. 3(1), 95 (2020). [CrossRef]
29. D. Yun, N. A. Malarich, R. K. Cole, S. C. Egbert, J. J. France, J. Liu, K. M. Rice, M. A. Hagenmaier, J. M. Donbar, N. Hoghooghi, S. C. Coburn, and G. B. Rieker, “Supersonic combustion diagnostics with dual comb spectroscopy,” Proc. Combust. Inst. 39(1), 1299–1306 (2023). [CrossRef]
30. D. Peng, C. Gu, Z. Zuo, Y. Di, X. Zou, L. Tang, L. Deng, D. Luo, Y. Liu, and W. Li, “Dual-comb optical activity spectroscopy for the analysis of vibrational optical activity induced by external magnetic field,” Nat. Commun. 14(1), 883 (2023). [CrossRef]
31. C. Gu, X. Zou, Z. Zuo, D. Peng, Y. Di, Y. Liu, D. Luo, and W. Li, “Doppler velocimeter based on dual-comb absorption spectroscopy,” Photonics Res. 8(12), 1895 (2020). [CrossRef]
32. C. Gu, Z. Zuo, D. Luo, D. Peng, Y. Di, X. Zou, L. Yang, and W. Li, “High-repetition-rate femtosecond mid-infrared pulses generated by nonlinear optical modulation of continuous-wave QCLs and ICLs,” Opt. Lett. 44(23), 5848 (2019). [CrossRef]
33. G. Ycas, F. R. Giorgetta, E. Baumann, I. Coddington, D. Herman, S. A. Diddams, and N. R. Newbury, “High-coherence mid-infrared dual-comb spectroscopy spanning 2.6 to 5.2 µm,” Nat. Photonics 12(4), 202–208 (2018). [CrossRef]
34. P. J. Schroeder, M. J. Cich, J. Yang, W. C. Swann, I. Coddington, N. R. Newbury, B. J. Drouin, and G. B. Rieker, “Broadband, high-resolution investigation of advanced absorption line shapes at high temperature,” Phys. Rev. A 96(2), 022514 (2017). [CrossRef]
35. D. D. Lee, F. A. Bendana, A. P. Nair, D. I. Pineda, and R. M. Spearrin, “Line mixing and broadening of carbon dioxide by argon in the v3 bandhead near 4.2 µm at high temperatures and high pressures,” J. Quant. Spectrosc. Radiat. Transfer 253, 107135 (2020). [CrossRef]
36. D. Luckhaus and M. Quack, “High-resolution FTIR spectra of NO2 and N204 in supersonic jet expansions and their rovibrational analysis,” J. Mol. Struct. 293, 213–216 (1993). [CrossRef]
37. D. Hurtmans and M. Herman, “Integrated band intensities in N2O4 in the infrared range,” J. Quant. Spectrosc. Radiat. Transfer 50(6), 595–602 (1993). [CrossRef]
38. S. P. Sander, A. R. Ravishankara, D. M. Golden, C. E. kolb, M. J. Kurylo, and R. E. Huie, “Chemical Kinetics and Photochemical Data for Use in Atmospheric Studies,” Jet Propulsion Laboratoyy Pasadena(CA), (2003).
39. A. Wang and M. F. Modest, “Importance of Combined Lorentz-Doppler Broadening in High-Temperature Radiative Heat Transfer Applications,” J. Heat Transfer 126(5), 858–861 (2004). [CrossRef]
40. M. Hepp, R. Georges, and M. Herman, “Striking anharmonic resonances in N2O4: supersonic jet fourier transform spectra at 13.3, 7.9, 5.7 and 3.2 μm,” J. Mol. Struct. 517-518, 171–180 (2000). [CrossRef]
