REACTIONS OF C2H5 RADICALS WITH HBR AND BR AT 298 K AND MILLITORR PRESSURES

The rates of the reactions of ethyl radicals with HBr (k(7)) and with Pr atoms (k(8)) 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: k(7) = (6.67 +/- 0.14) x 10-(13) cm(3)/(molecule(.)s) and k(8) = (1.19 +/- 0.04) x 10-(11) cm(3)/(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 k(7) 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 k(7).