Visible and ultraviolet resonance enhance multiphoton ionization photoelectron spectroscopy of H2S in the one-photon wavelength region 143–158 nm

The Rydberg states of H2S have been investigated by multiphoton ionization, resonant enhanced at the two-photon and three-photon level (REMPI). The REMPI spectra (ion signal vs laser wavelength) are compared to the one-photon absorption spectrum. In addition, photoelectron spectra (PES) were collected at most of the absorption peaks in both the 2+1 and 3+1 REMPI processes. The vibrational state distribution of H2S+ formed by REMPI at a number of laser wavelengths is highly peaked at a single vibrational level. These intermediate Rydberg states could therefore be assigned on the basis of the PES. The REMPI-PES at other laser wavelengths were more complex probably because of perturbed intermediate Rydberg states. A comparison of the 2+1 and 3+1 REMPI wavelength scans shows significant peak intensity differences, which we attribute to the different Δl selection rules in the two- and three-photon absorption steps. New H2S 4p Rydberg states were observed in the two-photon resonance study, and a number of previously observed peaks have been reassigned on the basis of these results.