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 N₂ 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 1π_u orbital of N₂⁺ in all the alignment angles, the suboutmost 3σ_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 N₂²⁺:N⁺₂ for the parallel alignment to that for perpendicular alignment obtained, including the 3σ_g orbital, is closer to the experimental result than that without considering this orbital.