Line-mixing between rotational Stark components of CH₃F self-perturbed and perturbed by helium: Experimental results and IOS analysis

Self- and He-broadening coefficients of microwave transitions of CH ₃F have been measured with and without the presence of an external electric field. This provides values for the J, K → J + 1, K (K = 0 - J) transitions for J = 1 and J = 3 as well as for the various J, K, M → J + 1, K, M′ (|M| = 0 - K, |M - M′| = 0, 1) Stark components. The results and those of a previous experimental study for pure CH₃F, which show significant line-mixing effects, are analyzed with a model based on the Infinite Order Sudden approximation. It is shown that the latter leads to very satisfactory modeling of observed values even though no parameter was adjusted since previously and independently determined basic cross-sections are used. The quality of the present predictions is comparable with that obtained previously with a semi-classical approach. Furthermore, it is shown that the previously stated inaccuracy of the IOS model was due to an oversimplified use of this approach.