Experimental studies, line-shape analysis and semi-empirical calculations of broadening coefficients for CH335Cl–CO2 submillimeter transitions

Abstract

Rotational transitions in CH335Cl mixed with CO2 are recorded at 296K and total pressures up to 0.6Torr in the frequency interval 186–901GHz (1.6–0.3mm) for J=6→7, 10→11, 17→18, 22→23, 31→32, 33→34 and K=0–6, using the frequency-modulation spectrometer of the Laboratory PhLAM (Lille, France). These line-shapes are analyzed with the commonly used Voigt profile as well as with more refined Speed-Dependent Voigt and Galatry models accounting for the line narrowing induced, respectively, by the speed-dependence of the relaxation parameters and by velocity-changing collisions. Due to the high line intensities, the fitting procedure involves the full implementation of the Beer–Lambert law instead of its traditional linear approximation. The experimentally deduced J- and K-dependences of the pressure-broadening coefficients are further used to obtain the model parameters of a semi-empirical approach allowing massive calculations of line-shape parameters for enlarged ranges of rotational quantum numbers requested by spectroscopic databases.