Theoretical study of H(D) + N₂O: Effects of pressure, temperature, and quantum-mechanical tunneling on H(D)-atom decay and OH(D)-radical production

RRKM calculations based on the theoretical BAC-MP4 potential energy data and molecular parameters for H(D) + N₂O reactions have been carried out by solving master equations which incorporate tunneling effect corrections for the H-atom (or D-atom) addition and migration processes. The generalized reaction mechanism involves an energetic adduct (HNNO^† or DNNO^†), which can redissociate back to the reactants, undergo an H-atom (or D-atom) migration to form products, or it could be stabilized via collisional deactivation. The thermal rate coefficients for the unimolecular decomposition and bimolecular chemical activation according to this mechanism were obtained from the numerical solution of master equations based on the Nesbet algorithm, microscopic reversibility, and Gaussian elimination, with the weak collision assumption using the exponential-down model. The convoluted effect of pressure and tunneling accounts for the observed curvature in the Arrhenius plots for the reactions of both H and D atoms. The calculated results are in excellent agreement with the experimental data of Marshall et al. (J. Phys. Chem. 1989, 93, 1922).