Effect of nuclear motion on tunneling ionization rates of molecules

Abstract

We show that the observable rate of tunneling ionization of a molecule in an intense low-frequency laser field is affected by nuclear motion and can essentially differ from a bare electronic characteristic calculated for fixed nuclei. Both the absolute value of the rate and the shape of its orientation dependence are affected. The effect is significant for $I\ensuremath{\sim}{10}^{14}$ W/cm${}^{2}$ and becomes more pronounced at lower intensities. An isotope effect in tunneling ionization of H${}_{2}$ and D${}_{2}$ is predicted. The results are compared with available experiments.