A reinvestigation of the Rydberg states of H2S and D2S by two-photon resonant multiphoton ionisation spectroscopy

Abstract

The technique of 2 + 1 resonance-enhanced multiphoton ionisation spectroscopy has been applied to the molecules H₂S and D₂S. Spectroscopic analysis provides the first definitive experimental evidence for the three series associated with electron excitation from the 2b₁ highest occupied molecular orbital to the p Rydberg functions, and for at least one nf â†� 2b₁ series. The results point to flaws in all previous analyses of the H₂S vertical electronic spectrum which, when corrected, allow an overall interpretation of the Rydberg states that is in excellent accord with the results of the most recent ab initio calculations of Galasso (J. Phys. B, 1989, 22, 2241). Additional features, evident in absorption and in MPI spectra recorded at higher light intensities, are ascribed to vibronic structure, the detailed interpretation of which must await a better knowledge of the lowest-lying (substantially valence) states derived as a result of electron promotion from the 2b₁ and 5a₁ molecular orbitals.