Reaction F + C 2 H 4 : 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 + C2 H4 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 C2 H4 , was found to be temperature independent in the temperature range used. H, C2 H3 F, and HF were identified as the reaction products. Absolute measurements of the yields of these species allowed to determine the branching ratios, k1b / k1 = (0.73 ± 0.07) exp(-(425 ± 45)/ T) and k1a / k1 = 1 - (0.73 ± 0.07) exp(-(425 ± 45)/ T) and partial rate constants for addition-elimination (H + C2 H3 F) and H atom abstraction (HF + C2 H3 ) pathways of the title reaction: k1a = (0.80 ± 0.07) × 10-10 exp(189 ± 37/ T) and k1b = (1.26 ± 0.13) × 10-10 exp(-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 k1a and k1b . The kinetic and mechanistic data from the present study are discussed in comparison with previous absolute and relative measurements and theoretical calculations.