Line-shapes and broadenings of rotational transitions of CH335Cl in collision with He, Ar and Kr

- Analysis of the speed dependence of relaxation rates on CH3Cl lines.
- Examination of the optical diffusion contribution.
- Measurement of collisional broadenings with a frequency-modulation technique.

Rotational lines of methyl chloride CH335Cl in collision with He, Ar, and Kr have been recorded at room temperature in the 186-901 GHz range (6.2-30.1 cm−1) for J=6→7, 10→11, 17→18, 22→23, 31→32, 33→34 and K=0-6. Owing to the high sensitivity of the frequency-modulated spectrometer used, clear deviations of the recorded line-shapes from the usual Voigt profile have been observed and their additional analyses with more refined models (Speed-Dependent Voigt, Galatry and Speed-Dependent Galatry profiles) have been performed. It has been evidenced that the observed line-shapes are mainly governed by the speed-dependence of relaxation rates (“wind effect”) and that the optical diffusion related to velocity changing collisions (Dicke effect) has a nearly negligible role.