Distinguishing resonance symmetries with energy-resolved photoion angular distributions from ion-pair formation in O2 following two-photon absorption of a 9.3 eV femtosecond pulse
Abstract
We present a combined experimental and theoretical study on the photodissociation dynamics of ion-pair formation in O2 following resonant two-photon absorption of a 9.3 eV femtosecond pulse, where the resulting O+ ions are detected using 3-D momentum imaging. Ion-pair formation states of 3-g and 3g symmetry are accessed through predissociation of optically dark continuum Rydberg states converging to the B 2-g ionic state, which are resonantly populated via a mixture of both parallel-parallel and parallel-perpendicular two-photon transitions. This mixture is evident in the angular distribution of the dissociation relative to the light polarization, and varies with the kinetic energy release (KER) of the fragmenting ion-pair. The KER-dependent photoion angular distribution reveals the underlying two-photon absorption dynamics involved in the ion-pair production mechanism and indicates the existence of two nearly degenerate continuum resonances possessing different symmetries, which can both decay by coupling to ion-pair states of the same total symmetry through internal conversion.