Quasiclassical trajectory studies of N+OH, O+NH, and H+NO collisions using global ab initio potential energy surfaces

Renee Guadagnini, George C Schatz, Stephen P. Walch

Research output: Contribution to journalArticle

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Abstract

We present a quasiclassical trajectory study of the collisions which occur on the 1A′, 3A″, and 1A″ potential surfaces of HNO using recently developed global potential surfaces that were derived from ab initio calculations. Each of these surfaces was assumed to be uncoupled from the other surfaces for the purposes of the calculations, and the appropriate statistical average of electronic states for each process was calculated. For N+OH and O+NH, we specifically studied reactive collisions which give H+NO as products, and we also studied the production of N+OH from O+NH. Overall rate constants calculated for either N+OH or O+NH are in good agreement with most experiments, and in addition, the product NO vibrational distribution from the N+OH reaction is in good correspondence with recent measurements, revealing modest excitation that is close to what would be expected from a statistical distribution. For O+NH, the calculated NO vibrational distributions are much hotter than statistical, in apparent disagreement with recent measurements. However, a careful analysis of limitations on the measurements due to spectral interference and to collisional relaxation indicates that it is not possible to say if theory and experiment are at odds for this reaction. We find a significant cross section for O+NH→N+OH on the 3A″ surface (roughly 5% of the total reactive cross section, independent of energy), and this leads to rate constants at low temperatures that are orders of magnitude higher at low temperature than estimates made earlier based on H atom abstraction on the 5Π surface. The mechanism of this reaction is found to involve three steps: addition to form HNO, isomerization to HON, and dissociation to produce N+OH. We have also studied nonreactive vibrational and rotational excitation in H+NO collisions, and we obtain distributions that are somewhat closer to experiment than obtained in previous theoretical studies, although there are still points of disagreement. We find that reactive H+NO→N+OH collisions have absolute cross sections and average NO rotational excitation that are in excellent agreement with recent fast H atom measurements.

Original languageEnglish
Pages (from-to)784-791
Number of pages8
JournalJournal of Chemical Physics
Volume102
Issue number2
Publication statusPublished - 1995

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Potential energy surfaces
potential energy
Trajectories
trajectories
collisions
Rate constants
Atoms
Experiments
cross sections
Electronic states
Isomerization
excitation
products
statistical distributions
Temperature
isomerization
atoms
dissociation
interference
estimates

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

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Quasiclassical trajectory studies of N+OH, O+NH, and H+NO collisions using global ab initio potential energy surfaces. / Guadagnini, Renee; Schatz, George C; Walch, Stephen P.

In: Journal of Chemical Physics, Vol. 102, No. 2, 1995, p. 784-791.

Research output: Contribution to journalArticle

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abstract = "We present a quasiclassical trajectory study of the collisions which occur on the 1A′, 3A″, and 1A″ potential surfaces of HNO using recently developed global potential surfaces that were derived from ab initio calculations. Each of these surfaces was assumed to be uncoupled from the other surfaces for the purposes of the calculations, and the appropriate statistical average of electronic states for each process was calculated. For N+OH and O+NH, we specifically studied reactive collisions which give H+NO as products, and we also studied the production of N+OH from O+NH. Overall rate constants calculated for either N+OH or O+NH are in good agreement with most experiments, and in addition, the product NO vibrational distribution from the N+OH reaction is in good correspondence with recent measurements, revealing modest excitation that is close to what would be expected from a statistical distribution. For O+NH, the calculated NO vibrational distributions are much hotter than statistical, in apparent disagreement with recent measurements. However, a careful analysis of limitations on the measurements due to spectral interference and to collisional relaxation indicates that it is not possible to say if theory and experiment are at odds for this reaction. We find a significant cross section for O+NH→N+OH on the 3A″ surface (roughly 5{\%} of the total reactive cross section, independent of energy), and this leads to rate constants at low temperatures that are orders of magnitude higher at low temperature than estimates made earlier based on H atom abstraction on the 5Π surface. The mechanism of this reaction is found to involve three steps: addition to form HNO, isomerization to HON, and dissociation to produce N+OH. We have also studied nonreactive vibrational and rotational excitation in H+NO collisions, and we obtain distributions that are somewhat closer to experiment than obtained in previous theoretical studies, although there are still points of disagreement. We find that reactive H+NO→N+OH collisions have absolute cross sections and average NO rotational excitation that are in excellent agreement with recent fast H atom measurements.",
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