Experimental studies by complementary terahertz techniques and semi-classical calculations of N₂- broadening coefficients of CH₃³⁵Cl

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• 作者：M. Guinet^a ; ^{Mickael.Guinet@univ-littoral.fr} ; F. Rohart^b ; J. Buldyreva^c ; V. Gupta^c ; ^d ; S. Eliet^a ; R.A. Motiyenko^b ; L. Margulè ; s^b ; A. Cuisset^a ; F. Hindle^a ; G. Mouret^a
• 关键词：N2-broadening coefficient ; CH3Cl ; CW-THz photomixing ; Submillimeter frequency-multiplication ; Speed-dependence ; Semi-classical calculation ; Exact trajectory ; J and K dependencies
• 刊名：Journal of Quantitative Spectroscopy and Radiative Transfer
• 出版年：2012
• 期刊代码：70_00224073
• 类别：ch
• 出版时间：July, 2012
• 卷：113
• 期：11
• 页码：1113-1126
• 文件大小：699 K

摘要

Room-temperature N₂-broadening coefficients of methyl chloride rotational lines are measured over a large interval of quantum numbers (6鈮?em>J鈮?0, 0鈮?em>K鈮?8) by a submillimeter frequency-multiplication chain (J鈮?1) and a terahertz photomixing continuous-wave spectrometer (J鈮?1). In order to check the accuracy of both techniques, the measurements of identical lines are compared for J=31. The pressure broadening coefficients are deduced from line fits using mainly a Voigt profile model. The excellent signal-to-noise ratio of the frequency-multiplication scheme highlights some speed dependence effect on the line shape. Theoretical values of these coefficients are calculated by a semi-classical approach with exact trajectories. An intermolecular potential including atom-atom interactions is used for the first time. It is shown that, contrary to the previous theoretical predictions, the contributions of short-range forces are important for all values of the rotational quantum numbers. Additional testing of modifications required in the semi-classical formalism for a correct application of the cumulant expansion is also performed. It is stated that the use of the cumulant average on the rotational states of the perturbing molecule leads, for high J and small K values, to slightly higher line-broadening coefficients, as expected for the relatively strong interacting CH₃Cl-N₂ system. The excellent agreement between the theoretical and the experimental results ensures the reliability of these data.