High-resolution studies of the electronic spectra of H2S and D2S

Abstract

The complementary techniques of high-resolution vacuum ultraviolet absorption spectroscopy and resonance-enhanced multiphoton ionisation spectroscopy have been employed in a reinvestigation of the vertical electronic spectra of the molecules H₂S and D₂S. In accord with previous, lower-resolution, absorption studies of H₂S the major part of the spectra of both isotopic species may be understood in terms of Rydberg series that arise from promotion of an electron from the highest occupied 2b₁ molecular orbital. The electronic symmetries of states involved in six Rydberg series have been established unambiguously through observation of the (partially resolved) rotational structure that accompanies their excitations. A number of additional resonances observed only in the multiphoton ionisation spectra are tentatively attributed to excitations involving Rydberg orbitals comprised predominantly of f and/or g functions. Several of the absorption features (most notably those involving excited sites of B₁ symmetry) exhibit anomalous intensity distributions between the various rotational branches. L-uncoupling and/or rovibronic level dependent predissociation are suggested as contributory causes.