Static-field effects on the ionization of a sinusoidally driven weakly bound electron

The role of a static field in the classical, stochastic ionization of the stretched hydrogen atom, interacting with a microwave field, is studied. Field-dependent action-angle variables are constructed and the effect of the microwave field is treated perturbatively in terms of the new canonical variables. The threshold for the onset of irregular motion is calculated using the Chirikov resonance-overlap criterion. This value for the critical ac field is seen to be nontrivially modified by the additional static field, though the change is inadequate to explain discrepancies with experiment. © 1987 The American Physical Society.