A quasiclassical trajectory study of H+N2O (nu(1),nu(2),nu(3))

We present a quasiclassical trajectory study of state resolved cross sections, rate coefficients, and product energy partitioning for the reaction H + N2O using a potential surface which is based on nb initio calculations, This surface allows for hydrogen attack on either end of N2O, 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 nor sufficient to explain the discrepancy. We also examine cross sections for different N2O 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.