Photoionization of the E F excited state of H2: Calculation of vibrational branching ratios and photoelectron angular distributions

Abstract

Vibrational branching ratios and photoelectron angular distributions have been calculated for photoionization from the lowest vibrational levels of the EF state in H₂. The Rydberg‐continuum dipole transition moments have been evaluated in the Coulomb approximation and the oscillator strengths have been calculated with the multichannel quantum defect method. Rovibronic coupling between continuum final‐state channels has been included and rotational/vibrational preionization is also accounted for where it arises. Only minor deviations from the Franck–Condon principle are predicted, primarily related to the promotion of the pσ_u Rydberg (continuum) orbital. This result disagrees somewhat with the (2+1) REMPI experiment of Anderson, Kubiak, and Zare (1984) near 18.5 eV. On the other hand, the results obtained in a (4+1) REMPI experiment by Cornaggia et al. (1986) at 15.7 eV are correctly reproduced. The possible influence of doubly excited configurations on the photoelectron distributions in various REMPI experiments in H₂ is discussed.