A new potential surface and quasiclassical trajectory study of H+H{sub 2}O{yields}OH+H{sub 2}
- Department of Chemistry, Northwestern University, Evanston, Illinois 60208-3113 (United States)
- Institute of Chemistry, Chemical Research Center, Hungarian Academy of Sciences, H-1525 Budapest, P.O. Box 17, (Hungary)
- Theoretical Chemistry Group, Argonne National Laboratory, Argonne, Illinois 60439 (United States)
We present a method for developing potential-energy surfaces for abstraction reactions with four or more atoms which combines spline fits to high quality ab initio results for the three degrees of freedom that are most active in the reaction (two stretches and a bend) with simple empirical functions (Morse stretches, cosine bends, and torsions) for the spectator variables. The geometry and force constants associated with the spectator modes are allowed to vary along the reaction path so as to match stationary point properties from the ab initio calculations. In an application of this approach to the H+H{sub 2}O reaction, we are able to generate a global surface for the H{sub 3}O system that accurately matches ab initio properties, and is globally smooth and free of artifacts. Quasiclassical trajectory (QCT) calculations are used with this surface to study the H+H{sub 2}O reaction dynamics for both the ground and local mode excited states. The resulting ground-state angular distributions, product state vibrational and rotational distributions, and rotational alignment factors are in excellent agreement with all known experiments. This represents an improvement over the results obtained using previous surfaces, but like the past surfaces, the calculated integral cross sections are below experiment by at least a factor of 2. For studies of the H+H{sub 2}O reaction involving local mode excited states of water, the new surface is consistent with ab initio threshold behavior, with the (04){sup -} local mode state having zero activation energy. However the reactive rate coefficients are substantially smaller than the observed total reactive plus inelastic rate coefficient. This indicates that recent experiments due to Barnes, Sharkey, Sims, and Smith are dominated by energy transfer rather than reaction. (c) 2000 American Institute of Physics.
- Research Organization:
- Argonne National Laboratory (ANL), Argonne, IL
- OSTI ID:
- 20217330
- Journal Information:
- Journal of Chemical Physics, Vol. 113, Issue 8; Other Information: PBD: 22 Aug 2000; ISSN 0021-9606
- Country of Publication:
- United States
- Language:
- English
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