Computational investigation of the isomers formed from the reaction S2 + O2

The reaction of disulfur (S-3(2) ) with oxygen S-3(2) +( 3)O2 is an important reaction in sulfur combustion leading to different S-1(2) O-2 isomers and subsequent intramolecular isomerization reactions. In this work reaction paths and products resulting from the reaction S-3(2) + (3)O2 are investigated computationally using four different quantum chemistry methods. The thermochemistry of the isomerization and dissociation reactions for species involved in this system is evaluated in detail and reported along with reaction paths and energy barriers. Enthalpies are calculated on CBS-QB3, G3B3, G4 levels of calculation and, whenever possible, on W1U levels. Entropy and heat capacity contributions versus temperature are determined from molecular structures, moments of inertia and vibrational frequencies. Importance of the reaction paths and kinetic parameters using bimolecular chemical activation analysis are estimated as function of temperature from the calculated thermochemical data. High pressure limit kinetic parameters are obtained from canonical transition state theory (TST) calculations. Results show that (SS)-S-1(=O)=O, (SO)-S-3, (SO2)-S-1 and 3S are the low energy products.