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The dissociative photoionization of CH 3 SSCH 3 has been investigated in the photon energy range of ϳ8-25 eV with a molecular beam/photoionization mass spectrometry/threshold photoelectron spectrometry system using synchrotron radiation as an ionization source. For dissociation above photon energy of 11.5 eV, six fragment ions of CH 3 ϩ , C 2 H 3 ϩ , SH 3 ϩ , HCS ϩ , S 2 ϩ , and CH 2 S 2 ϩ were reported for the first time. The photoionization efficiency spectra for the parent ion and for 12 observed fragment ions, CH 3 ϩ , C 2 H 3 ϩ , SH 3 ϩ , HCS ϩ , CH 2 S ϩ , CH 2 SH ϩ , CH 3 SH ϩ , CH 3 SH 2 ϩ , CH 3 SCH 2 ϩ , S 2 ϩ , CH 2 S 2 ϩ , and CH 2 S 2 H ϩ , were measured; their branching ratios as a function of photon energy were derived. Ionization energy of 8.20Ϯ0.04 eV for CH 3 SSCH 3 and the appearance energy for each fragment ion were determined from the onsets of the photoionization efficiency spectra. Based on the appearance energy and existing thermochemical data, plausible structures of the fragment ions and their neutral counterparts are proposed. Fragmentation mechanisms that involve H migration and structural rearrangement in the dissociative photoionization processes are discussed.

Monochromatic synchrotron radiation was used to excite selectively core electrons of the carbon and oxygen atoms in acetone, creating neutral core-excited resonance states. Electron energy spectra associated with Auger decay of three strong resonances were collected. The character of each resonance state was deduced through analysis of its decay spectrum.

Dissociation of vibrationally selected N2O+ in state C̃ 2Σ+ has been investigated with a threshold photoelectron−photoion coincidence technique in pulsed mode and with synchrotron radiation. Branching ratios and average releases of kinetic energy in channels of formation of fragments N+, O+, N2 +, and NO+ at a level below the threshold of state C̃ 2Σ+, and in levels (0,0,0), (1,0,0), and (0,0,1) of that state, were obtained from well-resolved time-of-flight peaks, fitted to Gaussian shape, in the coincidence mass spectra. The results show a vibrational energy dependence, in particular, competition between channels N+ + NO and N2 + + O. On the basis of the opposite trends of branching ratios and average releases of kinetic energy of these two channels at levels (1,0,0) and (0,0,1), the dissociation mechanism and energy partition upon dissociation are discussed.