Broadening, shift and depolarization of broad fine structure alkali spectral lines by helium

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Abstract
Due to the large values of the fine structure interval for the first resonance lines of Rb and Cs, we may treat separately the 2P1/2 and 2P3/2 atomic levels when perturbed by Helium atoms. Within the framework of semi-classical and impact approximations, and assuming an exchange interaction, the diffusion matrices S1/2 and S3/2 are numerically computed ; firstly by neglecting all 1/2 - 3/2 coupling, and secondly, by a more accurate treatment which makes use of the molecular potentials and shows that the D1-lines depolarization is entirely due to the short range nonadiabatic coupling. The validity of analytical approximate resolutions for asymptotic regions is studied, and also the trajectory for the P1/2 levels, correlated with a single molecular curve; the rectilinear assumption appears to be insufficient for very short range phenomena. The agreement with experimental results confirms that the exchange interaction predominates for intermediate distances