Computational investigation of the oxidation reactions of S$_3$ and S$_4$ with O$_2$

In this work, the reaction pathways and products resulting from the reactions $^1$S$_3$ + $^3$O$_2$ and $^1$S$_4$ + $^3$O$_2$ are investigated using three different quantum chemistry methods. The thermochemistry of formation, isomerization and degradation reactions for all species involved in these systems is evaluated in detail and the corresponding reaction profiles, including reactants, transition states, and products, are reported. Enthalpies are calculated at the CBS-QB3, G3, G4 levels of theory. Entropy and heat capacity contributions as functions of temperature are determined from the optimized molecular structures, moments of inertia and vibrational frequencies. Kinetic parameters are obtained using canonical transition state theory (TST) calculations. All reaction pathways in both systems ultimately lead to $^1$S$_2$O, $^3$SO, $^3$S, $^3$S$_2$, and $^1$SO$_2$ as final products. The calculations indicate that analogous reaction types in the two systems exhibit similar rate coefficients.