The interference minimum in the high-order harmonic spectrum of H2+ is studied by solving the full three-dimensional time-dependent Schrödinger equation for the electronic motion keeping the nuclei fixed. The two-center interference model works well when the internuclear distance is around its equilibrium value where also recombination to the 2Σg+ (1sσg) ground state dominates. As the internuclear distance is increased, the minimum first shifts in position compared with the prediction of the two-center interference model and subsequently disappears. These effects are caused by the excited 2Σu+ (2pσu) state, partly due to the interference between the amplitudes of recombination to the ground and excited states, but also partly due to the signal associated with recombination to the excited state alone. We find that at internuclear distances beyond R≃3 a.u. the signal close to the harmonic cutoff may be completely dominated by recombination into the excited 2Σu+ (2pσu) state.
Physical Review a (atomic, Molecular and Optical Physics), 2013, Vol 87, Issue 4