Single and double ionization of diatomic molecules in strong laser fields

Strong-field single ionization and double ionization of two diatomic molecules, O-2 and N-2, are studied and compared to Xe and Ar, using an intense ultrashort pulse Ti:sapphire laser in the 2x10(13) to 8x10(14) W/cm(2) intensity range. N-2 behaves Like a structureless atom for both single and double ionization. The recently reported suppression of the O-2(+) ion yield compared to Xe+ is confirmed in our experiment, but we show that the suppression is not due to dissociative recombination. Rather, we conclude that the ionization rate of O-2 is below that predicted by tunneling ionization. We extend the study to the double ionization of O-2 and find a distinctly reduced nonsequential double-ionization rate. We find evidence that electronic structure influences strong-field tunneling ionization in molecules. [S1050-2947(98)50512-4].