Rotationally resolved threshold photoionization of H2S

摘要

Threshold spectroscopy based on pulsed field ionization (PFI) has been used in conjunction with a VUV laser source to obtain the rovibronic distributions of molecular cations following single photon ionization. The technique selectively detects electrons produced from field ionization of very high-n Rydberg levels (n $GREQ 200) which lie within 1 - 2 cm$+$MIN@1$/ of each rovibronic threshold. Since the oscillator strength is continuous across an ionization threshold, the PFI spectrum reflects the rovibronic state population at threshold. The nascent rotational state distribution of the molecular ion reflects the exchanges of energy and angular momentum in the `scattering' of the photoexcited electron with the anisotropic molecular ion potential. Rotationally resolved studies on several molecular systems (O$-2$/, HCl, OH(OD), H$-2$/O and N$-2$/O) have shown that photoionization can lead to large changes in core rotation, e.g., $Delta@J $EQ J$+$PLU$/ -J' $LSEQ 5 for O$-2$/$+$PLU$/, when accompanied by ejection of photoelectrons with high orbital angular momentum (l $GREQ 3). For photoionization of nonlinear molecules (H$-2$/O), transitions between asymmetric top levels involving the rotational angular momentum projections, K$-a$/,K$- b$/,K$-c$/, permit resolution of the photoelectron continua according to symmetry. PFI studies on the van der Waals dimer, Xe$-2$/, demonstrate the utility of this technique for investigating low frequency vibrations in molecular cations and for studying minor species ($LSEQ 1%) in molecular beams.