Charge-resonance-enhanced ionization of diatomic molecular ions by intense lasers

We study the ionization of the ${\mathrm{H}}_2^{+}$ molecular ion in intense, short-pulse laser fields by numerically solving the three-dimensional time-dependent Schrödinger equation as a function of internuclear distance $R$. Anomalously high ionization for the molecular ion at large internuclear separations is observed for orientations parallel to the linearly polarized laser field. The ionization rate is found to exhibit maxima at large $R$, exceeding the atom limit by an order of magnitude. This is attributed to transitions between pairs of chargeresonant states which are strongly coupled by the field in diatomic molecular ions. The effect is shown to also occur in higher odd-charge diatomic molecular ions and can be attributed to field-induced nonadiabatic transitions between the charge-resonant states and electron tunneling suppression by the instantaneous Stark field of the laser.