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Quantitative calculation of product rovibrational distributions from atom-diatom exchange reactions

journal contribution
posted on 2023-06-08, 07:50 authored by Richard J Marsh, Anthony J McCaffery, Mark Osborne
We describe a rapid, accurate method for calculating rovibrational distributions in diatomic products from elementary chemical reactions. The basis of the model is momentum interconversion at a critical configuration defined in terms of molecular dimensions of the species involved. This approach shares common elements with recent models of inelastic processes and the kinematic reactive model of Elsum and Gordon. We point out that these and related approaches represent a development of Newtonian mechanics equivalent to that followed in the conventional formulation of classical mechanics, but one in which motive force for change at the molecular level is attributed to dp/dt rather than to dV/dq. This leads to a particularly transparent form of mechanics that uses only familiar data such as bond length, mass, spectroscopic constants, and velocity, yet may be applied to the highly resolved single collision experiments of molecular reaction dynamics. We describe key aspects of the computational method, e.g., the definition of the critical configuration, the disposal of reaction enthalpy, the manner of assigning product vibrational states, and the way in which conservation of energy is ensured. Examples are chosen to illustrate the range of reactions to which the method may be applied. Each would represent a challenge to conventional theory. We show that velocity-angular momentum diagrams may be used to interpret data and to give physical insight into the origins of observed rotational distributions. Good agreement is obtained between experimental and calculated (v,j) distributions for a wide range of elementary reactions suggesting that our model, despite its simplicity, captures the principal physics of chemical change at the molecular level.

History

Publication status

  • Published

Journal

Journal of Physical Chemistry A

ISSN

1089-5639

Publisher

ACS Publications

Issue

45

Volume

107

Page range

9511-9521

Department affiliated with

  • Chemistry Publications

Full text available

  • No

Peer reviewed?

  • Yes

Legacy Posted Date

2012-02-06

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