Nonsequential double ionization of nonaligned diatomic molecules N₂ and O₂

Nonsequential double ionization (NSDI) processes of nonaligned diatomic molecules N₂ and O₂ are studied using the S-matrix theory. Our results show that the NSDI process significantly depends on the molecular symmetry and structure. The ratio of NSDI rate to single ionization rate as a function of the field intensity is obtained. It is found that N₂ behaves closely to its companion atom Ar in the ratios over the entire intensity range, while O₂ exhibits an obvious suppression effect, which is qualitatively consistent with the experiment.