Photodissociation dynamics of doubly excited Rydberg states of molecular hydrogen

Abstract

We have applied photofragment ion imaging to investigate the dissociation dynamics of low-lying, doubly excited states of molecular hydrogen. A doubly excited electronic state is one in which both of the hydrogen electrons reside in excited molecular orbitals. Two-step, two-color multiphoton excitation of H2, first via 201.8 nm, two-photon excitation into the E, F 1Σ+g(vE=0, J=1) state, followed by ∼563 nm, 1+m (m=1, 2) excitation through the B″ 1Σ+u(v=0, J=0, 2), D 1Πu(v=2, J=1, 2), and B′ 1Σ+u(v=4, J=0, 2) states provides a ready means of populating several low-lying doubly excited states of H2 at increasing internuclear separations. From these doubly excited repulsive states, both dissociation and autoionization processes are possible. Because the excitation energy remains relatively constant as each intermediate state is accessed, differences in the photodissociation dynamics via each state can be ascribed directly to the effects of changing internuclear separation and electronic symmetry of the intermediate and dissociative states. H+ fragments detected from each photodissociation pathway are distinguished by their differing velocities, determined from an ion image.