The geometries of the radicals HSOO, HOSO, HSO2 and HOOS have been opt
imized at the MP2 = FULL/6-31G level, and energies obtained with Gaus
sian-2 theory. Internal rotations and vibrational frequencies are anal
yzed. The results yield values of DELTAH(f,298) for the four doublet r
adicals of 111.5, -241.4, -141.4 and 58.9 kJ mol-1, respectively. Impl
ications for reactions of interest in combustion and atmospheric chemi
stry are discussed. The results are employed to derive DELTAH(f,0) for
CH3SOO, CH3OSO and CH3SO2 of 91.8, -222.6 and -199.4 kJ mol-1, respec
tively. The calculated CH3S-OO bond strength is in excellent accord wi
th a recent measurement.