Field-ionization rates of the hydrogen molecular ion

We calculate the quasienergies and wavefunctions of the hydrogen molecular ion perturbed by a strong external electric field. Results are obtained for static-field ionization rates of the lowest dressed states. The nonlinear Stark shifts are also calculated for weak and strong fields for a range of internuclear separations. Charge and current densities are obtained and used to explain the ionization resonance structure. The ionization currents are found to be very sensitive to field strength and internuclear distance. There is evidence of critical distances that indicate the validity of Coulomb explosion models and electron localization. However, for this system, the results do not agree well with simple over-barrier models of electron release. Multiphoton ionization rates of low-frequency intense laser fields are estimated by cycle averaging.