Theoretical Study on the Kinetics and Dynamics of the Reaction of HNO (3A ) with HO2 (2A )

In this study, the kinetics, dynamics and mechanism of the reaction of nitroxyl (paramagnetic HNO (3A )) with the ground state hydroproxy radical (HO2 (2A )) is theoretically investigated at the CBS-QB3 level of theory. Quantum mechanically proposed potential energy surface of HNO (3A ) + HO2 (2A ) reaction includes one energized intermediate. The ab initio results are used to investigate the rate constants by means of RRKM calculations along with stochastic one-dimensional chemical master equation (CME) [1] modeling and steady state assumption (RRKMSSA) [2]. The temperature and pressure dependence of the reaction over a wide range of temperature (300-3000 K) and pressure (0.1-2000 Torr) are studied. The major products of the title reaction in the stated temperature range studied are trans- HNOH, O2 (X3Σg -), HNOO (T) and OH (D). The master equation calculations determine negligible OH+HNOO formation due to the corresponding high energy barrier. No sign of pressure dependence was observed for the title reaction over the stated range of pressure. The calculated rate constants from the CME simulation (weak collision model) are compared with those obtained from RRKM-SSA that is based on strong collision assumption. Our results indicate that the strong collision assumption increases the calculated rate constant for the formation of the main product (HNOH+O2(X3Σg -)) at lower temperature and 1 atm, compared to the results of CME simulation, although the results are in good agreement at higher temperatures.