Alignment-dependent nonsequential double ionization of N2 in intense laser fields: The role of different valence orbitals

The alignment-dependent nonsequential double ionization (NSDI) of diatomic molecule N-2 in intense fields is studied using the S-matrix theory. Our results show that the valence orbitals play an important role in alignment-dependent NSDI process: in addition to the contribution from the outmost 1 pi(u) orbital of N-2+ in all the alignment angles, the suboutmost 3 sigma(g) orbital plays an important role at small alignment angles, which is more pronounced at high intensity. Taking into account the experimental alignment condition, the ratio of N(2)2+:N(+)2 for the parallel alignment to that for perpendicular alignment obtained, including the 3 sigma(g) orbital, is closer to the experimental result than that without considering this orbital.