Quantum-Chemical and Theoretical Kinetics Studies on the Gas-Phase Unimolecular Decomposition Reaction of Sulfur Hexafluoride, SF6

The aim of this study is to calculate the unimolecular rate coefficients for the unimolecular decomposition reaction of the industrially important molecule, SF6. The energies of stationary-points involved in the title reaction are calculated by the combination W1 method. Two main reaction paths are considered: SF6 -> SF5 + F (R1) and SF6 -> SF4 + F-2 (R2). Having information on energies and molecular properties of reactants and transition-states, RRKM statistical rate theory is used to compute the rate coefficients as a function of temperature and pressure. For the bond dissociation process R1, special version of RRKM theory, i. e., Variable reaction coordinate-transition state theory (VRC-TST) is employed. Although the reaction R1 is the dominant process over a wide range of pressure and temperature, but the reaction R2 could be significant at high temperatures. The following Arrhenius expressions are obtained for high-pressure limiting rate constants of reaction paths R1 and R2: k(infinity,1) = 5.71 x 10(16) s(-1) exp (-429.8 kJ mol(-1) /RT) k(infinity,2) = 2.14 x 10(16) s(-1) exp (-590.6 kJ mol(-1) /RT).