Molecular photoelectron angular distribution rotations in multi-photon resonant ionization of H2(+) by circularly polarized ultraviolet laser pulses.

We study effects of pulse durations on molecular photoelectron angular distributions (MPADs) in ultrafast circular polarization ultraviolet resonant ionization processes. Simulations performed on aligned H2 (+) by numerically solving time dependent Schrödinger equations show rotations of MPADs with respect to the molecular symmetry axes. It is found that in multi-photon resonant ionization processes, rotation angles are sensitive to pulse durations, which we attribute to the coherent resonant excitation between the ground state and the intermediate excited electronic state induced by Rabi oscillations. Multi-photon nonresonant and single photon ionization processes are simulated and compared which exhibit a constant rotation angle. An asymmetry parameter is introduced to describe the pulse duration sensitivity by perturbation theory models. Influence of pulse frequency detunings on MPADs is also investigated where oscillations of rotations are absent at long pulse durations due to nonresonance excitation.