Speed dependence of CH335Cl–O2 line-broadening parameters probed on rotational transitions: Measurements and semi-classical calculations

• Published in: Journal of quantitative spectroscopy & radiative transfer Vol. 130; pp. 304 - 314
• Main Authors: Buldyreva, J., Margulès, L., Motiyenko, R.A., Rohart, F.
• Format: Journal Article
• Language: English
• Published: Elsevier Ltd 01.11.2013
• Subjects: Air-broadening; Approximation; CH3Cl; Cross sections; Exact trajectory; Fittings; Frequency modulation; J and K dependencies; Mathematical analysis; O2-broadening; Radiative transfer; Rotational; Semi-classical calculation; Signal to noise ratio; Spectroscopy; Speed dependence; Submillimeter absorption; O2-broadening; Air-broadening; Submillimeter absorption; Frequency modulation; Speed dependence; CH3Cl; Exact trajectory; Semi-classical calculation; J and K dependencies
• DOI: 10.1016/j.jqsrt.2013.05.023
• ISSN: 0022-4073

Relaxation parameters for K-components (K≤6) of six J→J+1 rotational transitions (J=6, 10, 17, 22, 31 and 33) of CH335Cl perturbed by O2 are measured at room temperature with Voigt, speed-dependent Voigt and Galatry profiles in order to probe the speed-dependence effects. With respect to the previous study of CH335Cl–N2 system [Guinet et al., J Quant Spectrosc Radiat Transfer 2012;113:1113], higher active-gas pressures are reached, providing better signal-to-noise ratios, and the exact expression of the Beer–Lambert law is introduced in the fitting procedure, leading, among other advantages, to much more realistic low-pressure results. The broadening parameters of the considered lines are also computed by a semi-classical method for various relative velocities of colliders and the powers characterizing the dependence of the collisional cross-sections on relative speeds are deduced as functions of the rotational numbers J and K. Additional calculations performed with the Maxwell–Boltzmann distribution of velocities show no significant difference with the earlier results [Buldyreva et al., Phys Chem Chem Phys 2011;13:20326] obtained within the mean thermal velocity approximation. Weighted sums of the presently measured Voigt-profile O2-broadening parameters and of the previously published N2-broadening ones are calculated to yield experimental air-broadening coefficients for spectroscopic databases. •Analysis of the speed dependence of relaxation rates of CH3Cl lines.•Introduction of the Beer–Lambert law in analysis of line-shapes recorded by FM technique.•Comparison of Maxwell–Boltzmann averaging and mean thermal velocity calculations.•Estimation of air-induced broadening for CH3Cl rotational lines.