Ionisation of highly-excited atoms by electric fields. I. Classical theory of the critical electric field for hydrogenic ions

Abstract

An exact classical method is developed for the study of the critical ionisation of highly-excited hydrogenic ions by slowly varying applied electric fields, under the assumption of adiabatic invariance of the classical action integrals. Exact classical values of the critical field, the critical energy of the atom and the separation constant are determined for a wide range of values of the parabolic action integrals. Simple analytic fits accurate to within one per cent of these values are presented. For applications to real atoms, effects of tunnelling and level crossing must be included. Corrections are also required for low-l states of excited non-hydrogenic atoms and ions.