Stable CH3SCH2. (1), relevant to the high-energy chemistry of dimethyl sulfide, is prepared as an isolated species in the gas phase by flash-vacuum pyrolysis of CH3SCH2CH2ONO at 550 degrees C, collisionally activated dissociation of CH3SCH2CH2SCH3.+, and collisional neutralization of its CH3SCH2+ cation. Loss of methyl is the major dissociation of 1 on thermal or collisional excitation, requiring 104 kJ mol(-1) at the thermochemical threshold, Variable-time neutralization-reionization mass spectrometry is introduced and used to distinguish the dissociations of neutral 1 from those of its cation following collisional reionization with oxygen. The latter deposits similar to 270 kJ mol(-1) in the CH3SCH2+ ion formed due to collisional activation and moderate Franck-Condon effects, calculated as 36-40 kJ mol(-1). Ab initio calculations at the G2(MP2) level of theory give the adiabatic ionization energy of 1 as IE(a) = 6.84 eV and the enthalpy of formation of 1(+) as Delta H-f,H-298 = 809 kJ mol(-1).