Temperature dependence of rate coefficients and branching ratios for the NH2+NO reaction via microcanonical variational transition state theory

Calculations of the temperature dependence of the rate coefficient and product branching ratios in the NH + NO reaction have been performed using microcanonical varitational transition state theory (μVTST) in conjunction with Rice-Ramsperger-Kassel-Marcus (RRKM) theory. The calculations have utilized parameters from Walch's complete active space self-consistent field (CASSCF)/internally contracted configuration interaction (ICGI) calculations for the stationary points on the potential energy surface, together with simple Morse potentials for the minimum energy pathways of the entrance and the OH exit channels. The computed total rate coefficient (k) displays a negative temperature dependent between 300 and 3000 K, in good agreement with the results of direct kinetic measurements. The predicted values of the branching ratio for formation of OH (α) are strongly temperature dependent, increasing rapidly from 0.1 at room temperature to 0.85 at 3000 K. Sensitivity modeling indicates that the enthalpy of the products (HN + OH) is a critical quantity that needs to be determined more accurately in order to make genuinely quantitative predictions