Multichannel Gas-Phase Unimolecular Decomposition Reaction of C5-Perfluorinated Ketone, C5-PFK: Theoretical Kinetics Studies

In this research, the elementary process of thermal unimolecular decomposition of C5-PFK, as an alternative molecule for SF6, is studied theoretically. The energies of the reactants, transition states and products of the reaction are computed by the combination CBS-QB3 method. Next, the rate coefficients for the formation of various products at different temperatures and pressures are calculated by statistical rate theories such as RRKM and master equation formalism. For the bond dissociation processes, the rate coefficients are calculated by variable reaction coordinate-transition state theory (VRC-TST) which is a flexible transition-state version of RRKM theory. It is found that C–C bond dissociation processes and decomposition to C3F6 + CF3COF are main product channels. At temperature 500 K, the branching ratio of product channel C3F6 + CF3COF is calculated to be about 25%. However, as temperature increases, the branching ratio of the latter reaction deceases to reach a value of about 0.5% at 2000 K. The major product channel at all conditions is dissociation to CF3CFCF3 + CF3C(O).