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Quantum mechanical reactive scattering for three-dimensional atom plus diatom systems. II. Accurate cross sections for H+H_2

Schatz, George C. and Kuppermann, Aron (1976) Quantum mechanical reactive scattering for three-dimensional atom plus diatom systems. II. Accurate cross sections for H+H_2. Journal of Chemical Physics, 65 (11). pp. 4668-4692. ISSN 0021-9606. http://resolver.caltech.edu/CaltechAUTHORS:20120808-115714441

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Abstract

Accurate three‐dimensional reactive and nonreactive quantum mechanical cross sections for the H+H_2 exchange reaction on the Porter–Karplus potential energy surface are presented. Tests of convergence in the calculations indicate an accuracy of better than 5% for most of the results in the energy range considered (0.3 to 0.7 eV total energy). The reactive differential cross sections are exclusively backward peaked, with peak widths increasing monotonically from about 32° at 0.4 eV to 51° at 0.7 eV. Nonreactive inelastic differential cross sections show backwards to sidewards peaking, while elastic ones are strongly forward peaked with a nearly monotonic decrease with increasing scattering angle. Some oscillations due to interferences between the direct and exchange amplitudes are obtained in the para‐to‐para and ortho‐to‐ortho antisymmetrized cross sections above the effective threshold for reaction. Nonreactive collisions do not show a tendency to satisfy a "j_z‐conserving" selection rule. The reactive cross sections show significant rotational angular momentum polarization with the m_j=m′_j=0 transition dominating for low reagent rotational quantum number j. In constrast, the degeneracy averaged rotational distributions can be fitted to statistical temperaturelike expressions to a high degree of accuracy. The integral cross sections have an effective threshold total energy of about 0.55 eV, and differences between this quantity and the corresponding 1D and 2D results can largely be interpreted as resulting from bending motions in the transition state. In comparing these results with those of previous approximate dynamical calculations, we find best overall agreement between our reactive integral and differential cross sections and the quasiclassical ones of Karplus, Porter, and Sharma [J. Chem. Phys. 43, 3259 (1965)], at energies above the quasiclassical effective thresholds. This results in the near equality of the quantum and quasiclassical thermal rate constants at 600 K. At lower temperatures, however, the effects of tunneling become very important with the quantum rate constant achieving a value larger than the quasiclassical one by a factor of 3.2 at 300 K and 18 at 200 K.


Item Type:Article
Related URLs:
URLURL TypeDescription
http://dx.doi.org/10.1063/1.432919DOIUNSPECIFIED
http://jcp.aip.org/resource/1/jcpsa6/v65/i11/p4668_s1PublisherUNSPECIFIED
Additional Information:© 1976 American Institute of Physics. Received 22 December 1975. Online Publication Date: 28 August 2008. We thank Ambassador College for generous use of their computational facilities. We also thank Professor Donald G. Truhlar for useful comments. Research supported in part by the United States Air Force Office of Scientific Research (Grant No. AFOSR-73-2539). Work performed in partial fulfillment of the requirements for the Ph. D. in Chemistry at the California Institute of Technology. Contribution No. 5251.
Funders:
Funding AgencyGrant Number
Air Force Office of Scientific Research (AFOSR)AFOSR-73-2539
Subject Keywords: HYDROGEN, ATOM−MOLECULE COLLISIONS, SCHROEDINGER EQUATION, THREE−DIMENSIONAL CALCULATIONS, CHEMICAL REACTION KINETICS
Other Numbering System:
Other Numbering System NameOther Numbering System ID
Caltech Arthur Amos Noyes Laboratory of Chemical Physics5251
Classification Code:PACS: 34.20.-b, 82.20.Kh
Record Number:CaltechAUTHORS:20120808-115714441
Persistent URL:http://resolver.caltech.edu/CaltechAUTHORS:20120808-115714441
Official Citation: Quantum mechanical reactive scattering for three‐dimensional atom plus diatom systems. II. Accurate cross sections for H+H2  George C. Schatz and Aron Kuppermann J. Chem. Phys. 65, 4668 (1976); http://dx.doi.org/10.1063/1.432919
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:33019
Collection:CaltechAUTHORS
Deposited By: Ruth Sustaita
Deposited On:08 Aug 2012 20:44
Last Modified:26 Dec 2012 15:53

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