Classical Stark mixing at ultralow collision energies

Exact solutions of the time-dependent classical equations are obtained for the full array of angular momentum mixing transitions nl --> nl' in atomic hydrogen induced by collisions with charged particles at ultralow energies. A novel classical expression for the transition probability P-l'l is prese nted. The exact classical results for P-l'l (alpha) as a function of l, l' and the Stark parameter alpha agree exceptionally well with (exact) quantal results. They complement the quantal results by revealing essential charac teristics which remain obscured in the quantal treatment.