A Quasiclassical Trajectory Study of H + N2O (ν1, ν2, ν3)

We present a quasiclassical trajectory study of state resolved cross sections, rate coefficients, and product energy partitioning for the reaction H + N 2 O using a potential surface which is based on ab initio calculations. This surface allows for hydrogen attack on either end of N 2 O, with N-atom attack giving an intermediate complex HNNO, which can then dissociate into NH + NO or undergo 1,3-hydrogen migration to produce OH + N 2 . O-atom attack, which involves a higher barrier than N-atom attack, leads only to direct reaction to form OH + N 2 . We find that the dominant mechanism for the production of OH + N 2 changes with energy, with N-atom attack being dominant near the threshold and O-atom attack becoming more important when that pathway becomes energetically accessible. At reagent translational energies of 2 eV, the OH + N 2 product is dominant by a factor of 15 over NH + NO, in reasonable agreement with experimental results. Our product OH and NH vibrational distributions also match the experiment, but the partitioning of energy between N 2 vibration−rotation and relative translation of OH + N 2 is seriously different. Factors which control this difference in energy partitioning are examined, and it is concluded that the difference in energy partitioning between O-atom attack and N-atom attack is not sufficient to explain the discrepancy. We also examine cross sections for different N 2 O initial states, and we find that N−N stretch is more effective than N−O stretch in enhancing overall reactivity near the OH + N 2 reactive threshold, while bend excitation is ineffective. At higher energies, N−O excitation becomes more effective as a result of the change in reaction mechanism from N-atom attack to O-atom attack, and N−N stretch excitation is ineffective. These results are in qualitative accord with recent mode-specific rate measurements. Our calculated thermal rate coefficients for formation of OH + N 2 are below measured values, but the agreement is much better for a slightly modified surface in which the barriers for O- and N-atom attack are lowered by 0.1 eV. The trajectory results indicate that O-atom attack rather than N-atom attack is the predominant reaction mechanism at temperatures above 700 K.