The classical limit of ionization in fast ion-atom collisions

Abstract
The authors study the classical-quantum correspondence for ionization in three-body fast ion-atom collisions. The existence of a classical limit of the quantum mechanical transition probabilities as a function of the momentum transferred to the electron during the collision, the impact parameter, the energy and angle of the emitted electron, and the initial quantum level of the target is investigated. A well behaved classical limit is shown to exist for large momentum transfers whereas ionization by small momentum transfers or at large impact parameters is shown to be classically suppressed. It is found that ionization at small impact parameters does not possess a well-defined classical limit. Modifications of classical trajectory Monte Carlo (CTMC) methods to account for non-classical ionization are suggested. Applications related to recent data for electron ejection into large angles are presented.