Experimental and theoretical studies of isomeric CH3S2 and CH3S+2.

By combining molecular beam photodissociation and photoionization measurements with ab initio Gaussian-2 (G2) calculations on the CH3S2 and CH3S+2 systems, we have shown that CH3SS is the dominant isomer formed in the photodissociation process, CH3SSCH3+hν(193 nm) →CH3S2+CH3. The experimental ionization energy for CH3SS (8.97±0.02 eV) and the heat of formation at 0 K for CH3SS+ (217.7±1.2 kcal/mol) are in excellent agreement with the G2 results. The photoionization efficiency spectrum observed for CH3SS is also consistent with the theoretical prediction that the Franck–Condon factor for the photoionization process, CH3SS+hν →CH3SS++e-, is not favorable. Based on the statistical modeling of experimental rates obtained previously for HS loss in the unimolecular decomposition of CH3SSCH+3 and the comparison with G2 ab initio predictions, we conclude that CH2SSH+ is most likely the isomer structure formed near the experimental appearance energy (11.07 eV) observed for the photodissociative ionization process, CH3SSCH3+hν→CH3S+2+CH3+e-. [ABSTRACT FROM AUTHOR]