Variable-time neutralization-reionization mass spectrometry was used to generate and detect the hypervalent radical dimethylsulfonium, (CH3)(2)SH. (1H(.)), and its isotopomers (CH3)(2)SD. (1HD(.)), (CD3)(2)SH. (1DH(.)), and (CD3)(2)SD. (1DD(.)). The successful detection of 1H(.)-1DD(.) was achieved in spite of severe interferences due to isobaric overlaps by the C-13, S-33, and S-34 isotope satellites of residual dimethylsulfide cation radicals. Radicals 1H(.)-1DD(.) dissociated by cleavages of the S-(H,D) and S-C bonds in a similar to 3:1 branching ratio. Ab initio calculations with large basis sets failed to find a local energy minimum for the (X)(2)A' ground electronic state of H-1(.), which dissociated without barrier to (CH3)(2)S and H. Several excited states of 1H(.) 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(.)-1DD(.) were ascribed to the properties of excited electronic states. (Int J Mass Spectrom 185/186/187 (1999) 639-649) (C) 1999 Elsevier Science B.V.
