One- and two-photon detachment of H- with excitation of H(n=2).

Abstract

The cross sections for one- and two-photon detachment of H{sup {minus}} with excitation of the degenerate H(2{ital s}) and H(2{ital p}) levels are calculated within an adiabatic hyperspherical representation. Both the partial cross sections, {sigma}(2{ital s}) and {sigma}(2{ital p}), and the photoelectron angular distribution asymmetry parameters are obtained. Our one-photon detachment results are dominated by the {sup 1}{ital P{ital o}} shape resonance feature above threshold, which is well known from prior theoretical and experimental work, with which our results are compared in detail. Our two-photon detachment cross sections and angular distribution asymmetry parameters exhibit a half-cycle of dipole-field-induced oscillation in the energy region from the H({ital n}=2) threshold to approximately 34 meV above threshold. The occurrence of a half-cycle of oscillation with significant amplitude over a 34-meV energy region above the H({ital n}=2) threshold is due to two circumstances unique to this two-photon process: first, in contrast to the strongly suppressed oscillations in the {sup 1}{ital S{ital e}} and {sup 1}{ital P{ital o}} attractive dipole-field channels for the H({ital n}=2)-{ital e}{sup {minus}} system, the amplitude of oscillation in the channel having {sup 1}{ital D{ital e}} symmetry is not strongly suppressed above threshold; second, electric dipole selection rules for the two-photonmore » process do not permit population of the intense {sup 1}{ital P{ital o}} shape resonance located above the H({ital n}=2) threshold, which would otherwise obscure the half-cycle of dipole-field-induced oscillation. For these reasons, the process of two-photon detachment of H{sup {minus}} is a favorable one for observing this dipole-field-induced oscillation above threshold, which has yet to be observed experimentally in any process.« less