Photoionization and Autoionization of H2

Abstract

The cross sections are calculated for direct photoionization and photoexcited autoionization of H₂ for light in the region 600–800 Å. Angular distributions of directly produced photoelectrons, lifetimes for vibrationally induced autoionization, some spectral assignments, and relative intensities of photoelectrons of various energies (from autoionizing states) are also given. The method by which the Rydberg and continuum state wavefunctions are derived is similar to the correlated pseudopotential method of Tully. The results indicate that correlation has only a small effect on the differential and total cross sections for photoionization. Agreement of theoretical and experimental lifetimes for autoionization is improved by the inclusion of correlation in the wavefunction. Critical tests of the calculations could be made by experimental study of the photoelectron spectra produced when H₂ is excited to certain specific autoionizing states; for these states, the theory predicts anomalously efficient autoionization associated with transfer of two vibrational quanta into electronic excitation.