Absolute Rate Constant and Product Branching Fractions for the Reaction between F and C2H4 at T = 202−298 K

Reaction F + C2H4: Rate Constant and Yields of the Reaction Products as a Function of Temperature over 298-950 K

The kinetics and products of the reaction of F + C₂H₄ have been studied in a discharge flow reactor combined with an electron impact ionization mass spectrometer at nearly 2 Torr total pressure of helium in the temperature range 298-950 K. The total rate constant of the reaction, k₁ = (1.78 ± 0.30) × 10^-10 cm³ molecule^-1 s^-1, determined under pseudo-first-order conditions, monitoring the kinetics of F atom consumption in excess of C₂H₄, was found to be temperature independent in the temperature range used. H, C₂H₃F, and HF were identified as the reaction products. Absolute measurements of the yields of these species allowed to determine the branching ratios, k_1b/ k₁ = (0.73 ± 0.07) exp(-(425 ± 45)/ T) and k_1a/ k₁ = 1 - (0.73 ± 0.07) exp(-(425 ± 45)/ T) and partial rate constants for addition-elimination (H + C₂H₃F) and H atom abstraction (HF + C₂H₃) pathways of the title reaction: k_1a = (0.80 ± 0.07) × 10^-10exp(189 ± 37/ T) and k_1b = (1.26 ± 0.13) × 10^-10exp(-414 ± 45/ T) cm³ molecule^-1 s^-1, respectively, at T = 298-950 K and with 2σ quoted uncertainties. The overall reaction rate constant can be adequately described by both the temperature independent value and as a sum of k_1a and k_1b. The kinetic and mechanistic data from the present study are discussed in comparison with previous absolute and relative measurements and theoretical calculations.