Quantum mechanical reactive scattering for three-dimensional atom plus diatom systems. II. Accurate cross sections for H+H2

George C Schatz, Aron Kuppermann

Research output: Contribution to journalArticle

298 Citations (Scopus)

Abstract

Accurate three-dimensional reactive and nonreactive quantum mechanical cross sections for the H+H2 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 "jz-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.

Original languageEnglish
Pages (from-to)4668-4692
Number of pages25
JournalJournal of Chemical Physics
Volume65
Issue number11
Publication statusPublished - 1976

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algae
Rate constants
Scattering
Atoms
Potential energy surfaces
Angular momentum
cross sections
scattering
atoms
Ion exchange
Polarization
thresholds
energy
Temperature
quantum numbers
reagents
tendencies
angular momentum
potential energy
interference

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics

Cite this

Quantum mechanical reactive scattering for three-dimensional atom plus diatom systems. II. Accurate cross sections for H+H2. / Schatz, George C; Kuppermann, Aron.

In: Journal of Chemical Physics, Vol. 65, No. 11, 1976, p. 4668-4692.

Research output: Contribution to journalArticle

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