Reactions of C2H5 radicals with HBr and Br at 298 K and millitorr pressures

Article abstract of DOI:10.1021/ja00136a014

The rates of the reactions of ethyl radicals with HBr (k₇) and with Br atoms (k₈) have been measured at 298 K and millitorr pressures using the Very Low Pressure Reactor (VLPR) technique. The rate constants at 298 K are the following: k₇ = (6.67 ± 0.14) × 10^-13 cm³/(molecule's) and k₈ = (1.19 ± 0.04) × 10^-11 cm³/(molecule's). Reaction 7 is a factor of about 14 times slower than had been reported in the only other two direct measurements made (Nicovich, J. M. et al. J. Phys.Chem. 1991, 95, 9890. Seakins, P. W. et al. J. Phys Chem. 1992, 98, 9847) which also reported a negative activation energy for k₇ of from -0.8 to -1.1 kcal/mol. Using broadly accepted thermochemistry for reaction 7 and reported values for the reverse reaction, it is shown that all reported data give a positive activation energy for k₇.