A gas-phase chemical activation technique employing the H and Cl abstraction reactions by methylene from chloromethanes has been developed for the production of chloroethanes in the energy range between 85 and 95 kcal mole−1. In this paper the results from the reaction of methylene with chloromethane are reported. The abstraction reactions serve as a clean source of methyl and chloromethyl radicals; combination of these radicals at 25°C produces C2H5Cl and 1,2-C2H4Cl2 at energies near 90 kcal mole−1. Since the critical energy for the unimolecular HCl elimination reactions is about 55 kcal mole−1, the molecules will react by this pathway unless deactivated by collisions with the bath molecules. By studying the system in the appropriate pressure ranges, the nonequilibrium rate constants were measured at 25°C as 3×109 and 1.8×108 sec−1 for C2H5Cl and 1,2-C2H4Cl2, respectively.

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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 × 107 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 1016.3–1016.9 sec−1 for isobutane and 1016.5–1016.9 sec−1 for neopentane.

Classical three-body trajectory calculations with LEPS potential surfaces have been done for F + FIR -» FH + R type reactions. The mass and other properties of the R body were adjusted to closely simulate the reaction with CH4 and CHsBr (or CH2CI2). The objective was to provide computed results, within the three-body approximation, which could be compared to experimental energy partitioning patterns for these two reactions and for reactions with CH3F, CH3OD, CH3CI, CH3I, and CHsHgCHs. The general pattern, i.e., release of ~60% of the energy as vibrational energy of HF, is reproduced by the LEPS surface. The computed results show only a small mass effect which appears as a slight broadening of the vibrational distribution. The calculations suggest that the HF(u = 3) population is quite sensitive to the thermochemistry, if the thermochemical limit is close to the HF(u = 3) energy. A significant fraction of the trajectories show complex (indirect) trajectories and also delayed secondary encounters. This feature is emphasized by the central light atom and suggests that care should be exercised in using the threebody approximation for hydrogen atom abstraction reactions. In the course of development of the trajectory computer program, calculations were done for the D + C1I reaction with an LEPS surface. Good agreement is found with experimental data for the DI channel, but the potential surface for the DC1 channel needs improvement.

The total decomposition rates of the chemically activated alkanes n-butane, n-pentane, isopentane, and neohexane were measured using an internal comparison technique. Chemical activation was by the C-H insertion reaction of excited singlet-state methylene radicals.A total of ten rate constants ranging from 4.6 X lo5 to 2.3 X lo' sec-' were measured for these alkanes at different excitation energies. These rates correlate via RRKM theory calculations with thermal A-factors in the range of to lo".' sec-' for free rotoractivated complex models and in the range of 1016.4 to sec-' for vibrator-activated complex models. I t was found that high critical energies for decomposition, "tight" radical models, and activated complex models with free internal rotations were required to correlate the decomposition rates of these alkanes with estimated alkyl radical recombination rates. The correlation is just barely possible even for these favorable extremes, indicating that there may be a basic discrepancy between the recombination rate and decomposition rate data for alkanes.