Arrhenius parameters for the decomposition reactions of various alkoxy radicals are eval-The recommended values for tert -butoxy radical decomposition reaction are uated. log A (s-l) = 14.1, E, = 15.3 kcal/mol.The parameters give reasonably self-consistent results with related rate constants, product distributions of hydrocarbon oxidation reactions, and the values reported in different laboratories in different environments.A reworking of data by Batt et al. on RO + NO and RO + NO2 leads to a lowering of his A factors for these reactions by a factor of 5. It also leads to a similar lowering of the A factors for RO decompositions. The intrinsic activation energies E for the addition of alkyl radicals R to the carbonyl group are not only found to be a function of the exothermicity of reaction, but they are also dependent on the nucleophilicity of the alkyl radicals. For each radical R (Me, Et, i-Pr) the data can be fit to an Evans-Polanyi plot E = a + b ( A f f ) , where a uniform slope b = 0.58 can be found for all R. The intercepts a are then found to decrease nearly linearly with the decreasing ionization potential of R, namely, a = 2.1 [IP] -6.2 (kcal/mol), with the ionization potential given in electron volts.

The high-pressure absolute rate constants for the decomposition of nitrosobenzene and pentafluoronitrosobenzene were determined using the very-low-pressure pyrolysis (VLPP) technique. Bond dissociation energies of DHo(C6Hs-NO) = 51.5 f 1 kcal/mole and DH" (C&s-NO) = 50.5 f 1 kcal/mole could be deduced if the radical combination rate constant is set at log k,(M-'.sec-') = 10.0 f 0.5 for both systems and the activation energy for combination is taken as 0 kcal/mole at 298'K. AH,O(CF,H~NO), AHjo(C+jF~NO), and Aff/'(C6F5') could be estimated from our kinetic data and group additivity. The values are 48.1 =t 1, -160 f 2, and -130.9 Z!Z 2 kcal/mole, respectively. C-X bond dissociation energies of several perfluorinated phenyl compounds, DHo(CsF5-X), were obtained from the reported values of AHjo(C6F&) and our estimated AHjo(C&5.) [X = H, CHB, NO, Cl, F. CFa, I, and OH].

The rate constant for tert-butyl radical recombination has been measured near 700°K by the very-low-pressure pyrolysis (VLPP) technique and was found to be 108.8*0.3 M-1.sec-1 with neglibible temperature dependence. The thermochemical parameters for tert-butyl radicals were varied within reasonable limits to bring into agreement the data for the decomposition of 2,2,3,3-tetramethyl butane and the recombination of terf-butyl radicals. The revised thermochemistry also makes the gas-phase results and liquid-phase results compatible.

The rates of reaction of hydrogen atoms with silane, germane, and (for comparison) ethylene have been determined at 20 Torr in a discharge flow system. The apparent bimolecular rate constants are 8.5 X 10~12, 4.3 X 10"10, and 3.5 X 10"13 cm3 molecule"1 sec"1, respectively, which are substantially larger than previously reported values. Activation energies were calculated by the empirical methods of Johnston (BEBO) and Spirin and compared with the values estimated from the experimental rate constants. The experimentally estimated values are lower than those predicted by the BEBO method, suggesting that the activated complex for reaction of hydrogen atoms with silane and germane may differ from the simple linear model for hydrogen atom transfer. * To whom correspondence should be addressed at Washington University.netic study of reactions of atomic hydrogen with the methane analogs silane and germane has been published until recently.3Recently reactions of hydrogen atoms,4 methyl radical,5 and trifluoromethyl radical6 with silicon and germanium hydrides and alkylsilanes have been reported. The results

The thermal decomposition of t-butylmethyl ether has been studied using the VLPP technique. The recommended Arrhenius parameters for the molecular elimination, reaction ( I ) , are A(800OK) = 1013,9 sec-I and E, (800'K) = 59.0 & 1.0 kcal/mole. No radical reactions occur under the conditions used. CH,These parameters are in good agreement with earlier experimental work and with theoretical estimates of both A and E.