Atmospheric Degradation of Two Hydrofluoroketones: Theoretical Rate Constants for the Gas-Phase OH-Oxidation of HFK-447mcc and HFK-465mc

Abstract

Accurate calculation of rate constants for gas-phase OH-oxidation reactions of fluorinated compounds is crucial for the understanding of atmospheric processes that are subject of the Kigali Agreement. Here, we have determined two such rate constants for two hydrofluoroketones, HFK-447mcc and HFK-465mc. The calculations were performed with a cost-effective multiconformer transition state theory protocol coupled with the constrained transition state randomization sampling method. The calculated rate constants of k(HO•+HFK-447mcc)=3.1×10−15cm3molecule−1s−1 and k(HO•+HFK-465mc)=3.2×10−14cm3molecule−1s−1 at 298.15 K imply an atmospheric lifetime of 10 years and 1 year, respectively. To our knowledge, these rate constants have never been determined experimentally or theoretically, and the similarity between the ratios of these two rate constants and of the well-studied acetone and diethyl ketone suggest the validity of our approach toward obtaining accurate rate constants and branching ratios.