The pyrolysis of NH3 was studied behind reflected shock waves at temperatures 2500–3000 K, using mass spectrometric analysis of dynamically sampled gas. The initial mixtures contained 0.14% to 6% NH3, with Kr as diluent, at total gas concentrations of about 2 × 10−6 mol cm−3. Concentration profiles of NH3, NH2, NH, and N2 were measured. It was found that the apparent rate coefficient for overall removal of NH3 is increased by increasing the initial NH3 concentration, but is decreased by addition of H2. Addition of H2 also suppressed NH, but left the NH2 concentration relatively unchanged. A close correlation was found between NH2 concentration and N2 formation rate, indicating that NH2 participates in the reaction which produces N2.The experimental results are consistent with a chain mechanism in which NH3 is removed by unimolecular decomposition and by attack by H, NH, and NH2. Computer analysis yields a rate constant of 1.2 × 1016 exp (−91 000 cal mol−1/RT) cm3 mol−1 s−1 for the unimolecular process.

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GEORGE PARASKEVOPOULOS and WING S. NIP. Can. J. Chem. 58,2146Chem. 58, (1980. Absolute rate constants of hydrogen and deuterium atom abstraction by O H and OD radicals from n-C4Hlo, n-C4Dlo, H, and D,, and by OH radicals from ~~O -C~H ,~ have been measured at room temperature in the gas phase using the flash photolysis-resonance absorption technique. The rate constants in units of cm3 mol-I s-I were found to be: The quoted errors are the 95% confidence limits. A kinetic isotope effect was observed when hydrogen was replaced by deuterium in the paraffin and Hz, whereas there was no significant effect when O H was replaced by OD.

Publication costs assisted by the Natlonal Research Council of CanadaAbsolute rate constants for the reactions of hydroxyl radicals with CHBF, CH2F2, CHF3, CH3CH2F, and CH3CHF2 at 297 f 2 K have been measured in t,he gas phase with the flash-photolysis resonance-absorption technique.The rate constants in units of cm3 mol-l s-l were kCHaF = (13.1 f 1.1) x io9, hCH2F2 = (7.05 f 0.84) x io9, kCHFS = (0.21 f 0.10) X lo9, ~C~~C H~F = (140 f 22) X lo9, and kcHsCHF2 = (22.3 f 2.2) X IO9. The quoted errors are the 95% confidence limits. The maximum potential influence of secondary reactions on the measured rates has been discussed and assessed to be less than 10% for all fluorocarbons except CHF, for which the reported value is an upper limit.

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