Quantal Stark mixing at ultralow collision energies

A new exact solution of the time-dependent quantal equation is obtained for the full array of angular momentum mixing transitions nl --> nl' in atomic hydrogen induced by collisions with charged particles at ultralow energies . Based on this new solution, efficient numerical procedures are devised. I t is proven that the present (fixed-frame) solution is equivalent to the ro tating-frame approach described by Kazansky and Ostrovsky (Kazansky A K and Ostrovsky V N 1996 Phys. Rev. Lett. 77 3094) and that it overcomes the dif ficulties therein. Analytic expressions for low quantum numbers it are pres ented. Numerical results for the transition array with n = 28 are reported.