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

Abstract

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 + F₂ (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_∞,1 = 5.71 × 10¹⁶ s⁻¹ exp (−429.8 kJ mol⁻¹ /RT)

k_∞,2 = 2.14 × 10¹⁶ s⁻¹ exp (−590.6 kJ mol⁻¹ /RT).