Kinetics of chemically activated isobutane and neopentane from the 4358- and 3660-å photolyses of diazomethane with propane and isobutane

The results of a study of chemically activated isobutane and neopentane produced by excited singlet-state methylene radical insertion into the secondary and tertiary C-H bonds of propane and isobutane, respectively, are reported. The methylene radicals were produced at two energies by the 4358- and 3660-Å photolyses of diazomethane. The measured decomposition rates for the energized isobutane are 1.9×10⁷ and 3.6×10 ⁷ sec^-1 in the 4358- and 3660-Å photolysis systems, respectively, and for the energized neopentane are 4.4×10⁶ and 6.8×10⁶ sec^-1 in the 4358- and 3660-Å photolysis systems, respectively. These rates correlate well via RRKM theoretical calculations with thermal A factors in the range of 10 ^16.3-10^16.9 sec^-1 for isobutane and 10 ^16.5-10^16.9 sec^-1 for neopentane.