Laser-induced electron recollision in H₂ and electron correlation

Single and double ionization processes are calculated for a 1D model of H₂ from numerical solution of the time-dependent Schrödinger equation in the presence of an intense I⩽5×10¹⁵ W∕cm², ultrashort (10 cycles) 800 nm laser pulse. Laser-induced electron recollision, LIERC, is identified from a systematic analysis of bound and continuum populations in the two-electron wave function. Recollision is shown to be responsible for double ionization at lower intensities, I<10¹⁵ W∕cm² and persists also in the first two excited states of H₂, the A ³Σ_u⁺ and B ¹Σ_u⁺ states. The effects of the symmetry (antisymmetry) of the two-electrons wave function is found to be dominant at large internuclear distances where enhanced ionization is operative, especially in the A ³Σ_u⁺, where the exclusion principle suppresses double ionization from LIERC. Furthermore, at large distances, double ionization is shown to occur with equal excitation of the highest occupied and lowest unoccupied molecular orbitals of the H₂⁺ core ion. Negligible core excitation occurs at equilibrium.