Interference asymmetry of molecular frame photoelectron angular distributions in bichromatic UV ionization processes

Abstract

We investigate molecular photoionization by ultrafast bichromatic linearly polarized UV laser pulses at frequencies 2w1 = perpendicular to the internuclear axis R involving π orbital excitation. Results from numerical solutions of time dependent Schrodinger equations for aligned H2+ show that molecular frame photoelectron angular distributions (MFPADs) exhibit signatures of asymmetry perpendicular to the molecular symmetry axis, arising from interference of coherent electron wave packets created by respectively one 2w and two-photon 21 w absorption. A resonant excitation process between the ground state and the excited state is triggered by the 1w pulse. The asymmetry of MFPADs varies periodically with pulse intensity I0 and duration T, which we attribute to coherent resonant Rabi oscillations in electronic state population. A perturbative model is adopted to qualitatively describe and analyze these effects in both resonant and nonresonant photoionization processes.