Lifetimes of Fluorinated Compounds

Rate constants for reactions of 11 hydrochlorofluorocarbons and 12 hydrofluorocarbons were measured by means of the absolute rate method over the temperature range 250-430 K. OH radicals were generated by flash photolysis, laser photolysis, or a discharge flow methods; and the concentration of OH radicals was monitored by means of the laser-induced fluorescence technique. The fluorinated compounds were purified by gas chromatography; impurities remaining in the samples after purification were found to have no sizeable effect on the measured rate constants. The Arrhenius rate expressions were determined from the kinetic data obtained in this study as well as from available literature data. A method for estimating rates of reactions with OH radicals using an artificial neural network method was developed. An algorithm for a back-propagation method for determining optimised weights was developed for cases in which the reactivities of individual reaction sites of a molecule are not known. The ability of the neural network method to predict rate constants was evaluated by using the leave-one-out method. Rate constants for 94 compounds, including hydrocarbons, hydrofluorocarbons, hydrochlorofluorocarbons, hydrochlorocarbons, and brominated compounds, were calculated within a factor of 2.