THE ELUSIVE DIMETHYLHYDROXYSULFURANYL RADICAL - AN INTERMEDIATE OR A TRANSITION-STATE

The stability and dissociations of dimethylhydroxysulfuranyl radical, a key intermediate in the atmospheric oxidation of dimethyl sulfide, have been investigated by neutralization-reionization mass spectrometry and ab initio calculations. Dimethylhydroxysulfuranyl radical (1) and its d6 derivative 2 were generated in the gas phase by neutralization of protonated dimethylsulfoxide and dimethylsulfoxide-d6, respectively. Hypervalent radical 1 dissociates completely within 4.5-mu-s to CH3SOH by loss of CH3. and to (CH3)2S by loss of OH.. These primary products undergo further extensive dissociations. 2 also shows a minor dissociation to (CD3)2SO by loss of hydrogen atom in addition to the formation of CD3SOH and (CD3)2S by losses of CD3. and OH., respectively. Ab initio calculations (MP4/6-31 G*) find no potential energy minimum for 1 that collapses without barrier by oxygen-sulfur or carbon-sulfur bond fissions. Vertical neutralization of ion 1+ produces an unstable radical 1 lying 193 kJ mol-1 above the lowest energy (CH3)2S and OH. products. Relative energies of all primary dissociation products were calculated and compared with experimental data.