Reactions of N(4S) atoms with NO and H2 have been investigated using direct detection of N atoms by the atomic resonance absorption technique in a shock tube apparatus, where N(4S) is generated by photodecomposition of NO by 193 nm laser radiation behind reflected shock waves. The rate constant of the reaction, N+NO→N2+O (1) has been determined using pseudo first-order kinetic analysis to be k1=(1.3±0.3)×1013 (cm3 mol−1 s−1) over 1600–2300 K temperature range, which agrees very well with the estimation by Baulch et al. [Evaluated Kinetic Data for High Temperature Reactions (Butterworths, London, 1973), Vol. 2]. No (or very small) activation energy of this process was confirmed. Also, the rate constant of the reaction, N+H2→NH+H (2) has been decided by adding H2 to NO–Ar mixtures; it is k2=(2.8±0.2)×1014 exp(−Ea/RT) (cm3 mol−1 s−1), where Ea =33±7 kcal/mol. A quantum mechanical calculation performed in order to determine the mechanism of this reaction suggests that the reaction N(4S)+H2→NH+H proceeds via a direct abstraction of H atom from H2, and it gives calculated activation energy which is in good agreement with the present experiment.
ArF laser photolysis in the mixtures of CH4 and O2 highly diluted in Ar has been conducted behind reflected shock waves, where O and H atoms have been monitored using the ARAS technique. The rate constant for the reaction CH4 + O → CH3 + OH (1) has been directly determined to be 10−8.95 ± 0.27 exp [−(15.4 ± 2.0)kcal mol−1/RT] cm3 molecule−1 s−1 over the temperature range of 1365–1840 K. Also the consecutive reactions; CH3 + O2 → CH3O + O (3a) and CH3 + O2 → CH2O + OH (3b) have been examined more directly than in previous thermally initiated experiments, and the combinations of k3a and k3b have been evaluated at the temperature range from 1622 to 1840 K.
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