Rate Constants for Abstraction of H from the Fluoromethanes by H, O, F, and OH

Abstract

In this work, we compiled and critically evaluated rate constants from the literature for abstraction of H from the homologous series consisting of the fluoromethanes (CH3F, CH2F2, and CHF3) and methane (CH4) by the radicals H atom, O atom, OH, and F atom. These reactions have the form RH + X → R + HX. Rate expressions for these reactions are provided over a wide range of temperatures (300-1800 K). Expanded uncertainty factors f (2σ) are provided at both low and high temperatures. We attempted to provide rate constants that were self-consistent within the series - evaluating the system, not just individual reactions. For many of the reactions, the rate constants in the literature are available only over a limited temperature range (or there are no reliable measurements). In these cases, we predicted the rate constants in a self-consistent manner employing relative rates for other reactions in the homologous series using empirical structure-activity relationships, used empirical correlations between rate constants at room temperature and activation energies at high temperatures, and used relative rates derived from ab initio quantum chemical calculations to assist in rate constant predictions.