Rate constants for the reactions of fluorine atoms with alkanes and hydrofluorocarbons at room temperature

Abstract

Rate constants for the reactions of F atoms with a number of C₁ and C₂ alkanes and fluoro-substituted alkanes (HFCs) have been determined at room temperature using a relative rate technique. Fluorine atoms were generated by continuous photolysis of F₂ in a mixture containing either (a) HCl and an alkane or substitued alkane, or (b) a mixture of two substituted alkanes. Changes in the concentrations of the two molecular reagents were measured via changes in their IR absorption spectra observed with a Fourier transform IR (FTIR) spectrometer. Relative rate constants were converted to absolute values using the previously measured rate constants for the reference reactions. The following rate constants were derived for 298 ± 4 K (in cm³ molecule^–1 s^–1, with 2σ errors quoted): CH₄(4.7 ± 1.0)× 10^–11; CFH₃(2.8 ± 0.6)× 10^–11; CF₂H₂(4.7 ± 0.9)× 10^–12; CF₃H (1.35 ± 0.3)× 10^–13; C₂H₆(1.7 ± 0.3)× 10^–10; CF₃CH₃(HFC-143a), (2.1 ± 0.8)× 10^–12; CF₃CFH₂(HFC-134a), (1.25 ± 0.4)× 10^–12; CF₃CF₂H (HFC-125), (3.65 ± 0.4)× 10^–13.