Quantum calculation of intramultiplet mixing: Comparison with simple radial and angular mechanisms

Cross sections for intramultiplet mixing in the lowest 2P states of alkali atoms (K, Rb, Cs) in collisions with He atoms are calculated in body fixed coordinates. The cross sections for transitions that maintain or change the magnitude of the projection of the electronic angular momentum are compared with very simple semiclassical models for radial (R1) and angular (R2) coupling of electronic states. The angular mixing model uses a hard sphere interaction. The agreement is good for the total cross sections and for the transition probabilities for different partial waves. The total cross sections are compared with experimental and other theoretical results, and cross sections are presented for collisions of polarized 2P3/2 atoms. The quantum mechanical equations are integrated with a constant step size Magnus method, and we find uniform convergence O(h2) for small step sizes. The error rapidly increases for steps large enough to allow propagation of a channel by half of a de Broglie wavelength.