Time-domain and tunneling pictures of nonadiabatic induced electron ejection in molecular anions

Molecular anions possessing excess internal vibrational and/or rotational energy can eject their "extra" electron through radiationless transitions involving non-Born-Oppenheimer coupling. In such processes, there is an interplay between the nuclear and electronic motions that allows energy to be transferred from the former to the latter and that permits momentum and/or angular momentum to also be transferred in a manner that preserves total energy, momentum, and angular momentum. There are well established quantum mechanical expressions for the rates of this kind of radiationless process, and these expressions have been used successfully to compute electron ejection rates. In this paper, we recast the state-to-state quantum rate equation into the time domain and into a form in which the departing electron tunnels through a radial potential. The time domain expressions are especially useful for polyatomic systems where the multidimensional time correlation function decays to zero on a very short time scale. The tunneling framework is more appropriate when the perturbative assumptions, upon which the time-domain expressions are based, are questonable.