Reactive scattering, atom-diatom

The cancellation in GP effects in the state-to-state DCS are found [20-22, 26, 27, 29] at low impact parameters, when F(J) in Eq. (15) is chosen to include only contributions for which / < 9. It is well known [55,56] that most of the reactive scattering in this regime consists of head-on collisions, in which the reaction proceeds mainly by the H atom striking the H2 diatom at geometries that are close to linear. Most of the products are then formed by direct recoil in the backward (9 = 180°) region, this being typical behavior for a hydrogen-abstraction reaction. 

We have already mentioned (expressions 30—33) the widely used LEPS surface for atom-diatom reactions. This may be regarded as purely empirical or semi-empirical in any modification in which some integrals are evaluated. Another system for which fairly elaborate potential functions have been used is for non-reactive atom-diatom scattering. The experiment for which the potential is designed is the change of rotational or vibrational state of a diatomic molecule by collision with a third atom, and also the quasi bound states, which may be observed spectroscopically, of van der Waals molecules such as Ar—H2 (133). 

Atom + Diatomic Molecule Reactions studied by Reactive Scattering [358]... 

Schatz, G. C. and Kuppermann, A. (1976) Quantum mechanical reactive scattering for three-dimensional atom plus diatom systems. I. Theory, J. Chem. Phys. 65, 4642-67. 

Light J.C. and Walker. E.B. (1976) An B matrix approach to the solution of coupled equations for atom-molecule reactive scattering, J. Chem. Phys. 65. 4272-4282. Halavee, U. and Shapiro, M. (1976) A collinear analytic model for atom-diatom chemical reactions, J. Chem. Phys. 64, 2826-2839. 

The development of theory for reliable calculations of chemical dynamics has two components the construction of accurate, ab initio, multidimensional potential energy surfaces (PESs) and the performance of reactive scattering calculations, either by time-independent (TI) or time-dependent (TD) methods, on these surfaces. Accurate TI quantum methods for describing atom-diatom reactions, in particular for the benchmark H + H2 reaction, have been achieved since 1975.[1,2,3] Many exact and approximate theories have been tested with the H + H2 reaction.[4,5]... 

L. Wolniewicz and J. Hinze, Atom-diatomic molecular reactive scattering Investigation of the hyperangular integration. J. Chem. Phys., 85 2012-2018, 1986. 

Atom-Diatom Resonances Within a Many-Body Approach to Reactive Scattering... 

We present in this subsection the TD treatment for calculating initial state-specific total reaction probabilities for the atom-diatom reaction, H + 02 - HO + O. This is a particularly important combustion reaction (86) and it presents a real challenge to theoretical calculations because the PES has a deep well of more than 2.3 eV which supports many bound states and narrow resonances. Much progress has been made in the past few years by Neuhauser et al. in TD calculation of atom-diatom reactive scattering... 

The following is a brief discussion of our TD treatment for a general atom-diatom reactive scattering system. 

In transition state theory it is assumed that a dynamical bottleneck in the interaction region controls chemical reactivity. Transition state theory relates the rate of a chemical reaction in a microcanonical ensemble to the number of energetically accessible vibrational-rotational levels of the interacting particles at the dynamical bottleneck. In spite of the success of transition state theory, direct evidence for a quantized spectrum of the transition state has been found only recently, and this evidence was found first in accurate quantum mechanical reactive scattering calculations. Quantized transition states have now been identified in accurate three-dimensional quantal calculations for 12 reactive atom-diatom systems. The systems are H + H2, D + H2, O + H2, Cl + H2, H + 02, F + H2, Cl + HC1, I + HI, I 4- DI, He + H2, Ne + H2, and O + HC1. 

A. Kuppermann, G. G Schatz, and M. Baer, Quantum Mechanical Reactive Scattering for Planar Atom Plus Diatom Systems. I Theory, J. Chem. Phys. 65 4596 (1976). 

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