Transition states for chemical reactions I. Geometry and classical barrier height

Malick, David K.; Petersson, G. A.; Montgomery, John A.

doi:doi:10.1063/1.476317

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Nearside–farside analysis of differential cross sections: Ar+N₂ rotationally inelastic scattering using associated Legendre functions of the first and second kinds

We have carried out the first nearside–farside (NF) analysis of angular scattering for molecular collisions in which the partial wave series for the scattering amplitude is expanded in a basis set of associated Legendre functions (of the first kind.) The practical implementation of the NF theory is described, which exploits in an essential way properties of associated Legendre functions of the second kind. The new concept of a restricted nearside–farside (resNF) decomposition of the scattering a...

A stochastic technique for solving the Lorentz–Boltzmann equation for hard spheres: Application to the kinetics of gas absorption

The Lorentz–Boltzmann equation for tagged particle motion in a hard sphere fluid may be interpreted as describing the motion of a particle propagating via a series of binary uncorrelated collisions in a structureless bath of fluid particles with a Maxwellian distribution of velocities. We describe a very general stochastic technique for solving the equation. The method can also be extended to the Enskog level, valid up to somewhat higher densities, by a simple scaling of the time. Having reprodu...

A new computational procedure for the characterization of transition states for chemical reactions is proposed and tested. Previous calculations have frequently employed a single point high-level energy calculation at a transition state geometry obtained with a less expensive computational method, Energy[Method(1)]//Geom[Method(2)]. If we instead search the “inexpensive” intrinsic reaction coordinate (IRC) for the maximum of Energy[Method(1)] along this reaction path, the resulting “IRCMax method”, Max{Energy[Method(1)]}//IRC{Geom[Method(2)]}, reduces errors in transition state geometries by a factor of 4 to 5, and reduces errors in classical barrier heights by as much as a factor of 10. When applied to the CBS-4, G2(MP2), G2, CBS-Q, and CBS-QCI/APNO model chemistries, the IRCMax method reduces to the standard model for the reactants and products, and gives rms errors in the classical barrier heights for ten atom exchange reactions of 1.3, 1.2, 1.0, 0.6, and 0.3 kcal/mol, respectively. © 1998 American Institute of Physics.

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KEYWORDS and PACS

Keywords

chemical reactions, molecular electronic states, molecular configurations, potential energy surfaces, perturbation theory

PACS

82.30.-b

Specific chemical reactions; reaction mechanisms
33.15.Bh

General molecular conformation and symmetry; stereochemistry
31.90.+s

Other topics in the theory of the electronic structure of atoms and molecules (restricted to new topics in section 31)