Photoionization of carbon disulfide monomers and dimers in a supersonic molecular beam

Photoionization efficiency curves have been obtained for CS2+ and (CS2)2+ using molecular beam sampling. The monomer was studied between 1005–1240 Å using an optical resolution of about 1.5 Å (12 meV at 1200 Å). The observed ionization potential of CS2(2π3/2 ground state) is 10.070±0.006 eV. A small number of steplike fine structure features are seen in the vicinity of threshold. This structure is identified with transitions to the 2π1/2 spin state (10.125±0.006 eV) and a few low energy vibrational levels of the ion. These features and the intense autoionization structure exhibited by this species are discussed. The photoion yield curve of (CS2)2+ was measured over the wavelength range 1000–1295 Å at an energy resolution of about 30 meV. Ionization is first observed at approximately 9.63 eV. The onset is very weak and the photoionization efficiency rises gradually with increasing photon energy. From the measured monomer and dimer ionization thresholds, a lower limit to the dimer ion binding energy is calculated to be 11.3 kcal/mole. In comparing monomer and dimer curves, a very close correspondence of autoionization features in the region 1000–1060 Å is observed. In contrast, autoionization structure which occurs in the photoion yield curve of CS2+ between 1100–1125 Å is either markedly shifted in energy and broadly distributed or entirely absent in the (CS2)2+ curve. These changes are interpreted in terms of the geometry of the CS2 dimer.