Static field tunneling ionization of H-2(+)

We present tunneling ionization rates from a double-well potential in the p resence of an external de electric field in order to better understand the behavior of molecules in strong laser fields. Our calculations confirm the well-established peak in the ionization rate as a function of internuclear separation at a critical separation R-max. However, we also find that R-max is a function of the external field strength F such that R-max(F)F is appr oximately constant. Because these numerical calculations make no assumption s beyond the shape of the potential well, we can test commonly used approxi mations to the shift in the energy levels as a function of internuclear sep aration and field strength. Finally, we find that the tunneling ionization rate is not a monotonic function of the field strength showing a pronounced minimum and thus is qualitatively different from tunneling ionization rate s in atoms. To our knowledge, this behavior has not been predicted previous ly for molecules in strong fields.