An experimental and theoretical study of the photoelectron spectrum of hydrogen selenide

The photoelectron spectrum of hydrogen selenide has been recorded using synchrotron radiation in the photon energy range 15-110 eV and the inner valence region has been studied in detail for the first time. Green's function methods have been employed to evaluate the ionisation energies and spectral intensities of all valence states and the results have facilitated an interpretation of the experimental spectra. Two outer valence satellites have been observed at binding energies of ∼17 and ∼18.5 eV. The continuum multiple scattering (CMS-Xα) approach has been used to calculate photoelectron asymmetry parameters and branching ratios for the outer valence orbitals and these have been compared with experimental data. The Se 4p Cooper minimum strongly affects the photoionisation dynamics of the outermost 4b1 orbital and its influence is evident in both the theoretically predicted and the measured asymmetry parameter for the X˜2B1 state. The experimental data for the A˜2A1 and B˜2B2 state asymmetry parameters also display energy dependent variations in the vicinity of the Cooper minimum. However, for these two states the agreement between the predicted and observed asymmetry parameters is less satisfactory. The present results for H2Se have been compared with similar data for the closely related H2S molecule.