PENNING IONIZATION OF CH3SCH3, CH3SSCH3, AND CH3CH2SH BY COLLISION WITH HE-ASTERISK(2(3)S) METASTABLE ATOMS

Penning ionization of CH3SCH3 (dimethyl thioether), CH3SSCH3 (dimethyl disulfide), and CH3CH2SH (ethyl thioalcohol) upon collision with He( 2(3)S) metastable atoms was studied by two-dimensional (electron-energ y/ collision-energy-resolved) Penning ionization electron spectroscopy . A collision energy dependence of the partial ionization cross sectio ns has indicated that the interaction potentials are anisotropic betwe en He(2(3)S) and the target molecules. For CH3SCH3 and CH3CH2SH, the interaction potential around the sulfur atom was found to be more attr active for the out-of-plane direction vertical to the CSC or CCS plane than for the in-plane direction, while the opposite trend was observe d around the oxygen atom of CH3CH2OH. Anisotropic potential for CH3SSC H3 was found to be similar to that for CH3SCH3. Strongly enhanced band s in Penning ionization electron spectra of sulfur compounds, which we re assigned to ionization from molecular orbitals having sulfur 3s (S- 3s) atomic orbital character, were found to be associated with an inte rmolecular excitation transfer from He to the target molecule and als o with the following intramolecular Auger-like autoionization process.