Metastable states of dimethylsulfonium radical, (CH_3)_2SH~(centre dot): a neutralization-reionization mass spectrometric and ab initio computational study

摘要

Variable-time neutralization-reionization mass spectrometry was used to generate and detect the hypervalent radical dimethylsulfonium, (CH_3)_2SH~(centre dot) (1H~(centre dot)), and its isotopomers (CH_3)_2SD~(centre dot) (1HD~(centre dot)), (CD_3)_2SH~(centre dot) (1DH~(centre dot)), and (CD_3)_2SD~(centre dot) (1DD~(centre dot)). The successful detection of 1H~(centre dot) - 1DD~(centre dot) was achieved in spite of severe interferences due to isobaric overlaps by the ~(13)C, ~(33)S, and ~(34)S isotope satellites of residual dimethylsulfide cation radicals. Radicals 1H~(centre dot) - 1DD~(centre dot) dissociated by cleavages of the S-(H,D) and S-C bonds in a approx 3:1 branching ratio. Ab initio calculations with large basis sets failed to find a local energy minimum for the (X)~2A' ground electronic state of 1H~(centre dot), which dissociated without barrier to (CH_3)_2S and H~(centre dot). Several excited states of 1H~(centre dot) were found by configuration interaction singles CIS/6-311 + + G(3df,2p) calculations that were within 2 eV of the repulsive ground state potential energy surface. The microsecond metastability and dissociations of 1H~(centre dot)-1DD~(centre dot) were ascribed to the properties of excited electronic states.