Four-atom reactions

Pogrebnya S K, Echave J and Clary D C 1997 Quantum theory of four-atom reactions using arrangement channel hyperspherical coordinates Formulation and application to OH + Hg < HgO + H J. Chem. Phys. 

Clary D C 1994 Four-atom reaction dynamics J. Phys. Chem. 98 10 678... 

FIRST PRINCIPLES QUANTUM DYNAMICAL STUDY OF FOUR-ATOM REACTIONS... 

First Principles Quantum Dynamical Study of Four-Atom Reactions... 

In the adiabatic bend approximation (ABA) for the same reaction,18 the three radial coordinates are explicitly treated while an adiabatic approximation was used for the three angles. These reduced dimensional studies are dynamically approximate in nature, but nevertheless can provide important information characterizing polyatomic reactions, and they have been reviewed extensively by Clary,19 and Bowman and Schatz.20 However, quantitative determination of reaction probabilities, cross-sections and thermal reaction rates, and their relation to the internal states of the reactants would require explicit treatment of five or the full six degrees-of-freedom in these four-atom reactions, which TI methods could not handle. Other approximate quantum approaches such as the negative imaginary potential method16,21 and mixed classical and quantum time-dependent method have also been used.22... 

An overview of the time-dependent wavepacket propagation approach for four-atom reactions together with the construction of ab initio potential energy surfaces sufficiently accurate for quantum dynamics calculations has been presented. Today, we are able to perform the full-dimensional (six degrees-of-freedom) quantum dynamics calculations for four-atom reactions. With the most accurate YZCL2 surface for the benchmark four-atom reaction H2 + OH <-> H+H2O and its isotopic analogs, we were able to show the following ... 

Clearly the difficult first principles theoretical study of four-atom reactions, particularly the prototype benchmark H2 + OH <-> H + H2O reaction and its isotopic analogs, has reached as exciting a level as when the first report of... 

We mention, in addition, that complete and highly accurate ab initio11 theoretical solutions for a number of simple atom-diatom reactions like H + HD —> H2 + D have been obtained. Recently, the quantum dynamics of the four-atom reaction H2 + OH —> H20 + H and its reverse has also been reported [9,10], The general features of these results at the level of k(T) will typically agree fairly well with the quasi-classical approach, provided the temperature is sufficiently high so that quantum mechanical tunneling is negligible. 

Clary, D.C. (1994) Four-atom reaction dynamics, J. Phys. Chem. 98, 10678-10688. Pack, R.T. and Parker, G.A. (1987) Quantum reactive scattering in three dimensions using hyperspherical (APH) coordinates. Theory, J. Chem. Phys. 87, 3888-3921. Truhlar, D.G., Mead, C.A. and Brandt, 5I.A. (1975) Time-Reversal Invariance, Representations for Scattering Wavcfunctions, Symmetry of the Scattering Matrix, and Differential Cross-Sections, Adv. Chem. Phys. 33, 295-344. 

Four-atom reactions came into focus with the development by Clary of the Rotating Bond Approximation (RBA)[10. 11] and Bowman s reduced-dimensionality adiabatic bend (RD-AB) calculations of four-atom reactions. In the latter three stretching vibrational motions are treated explicitly quantum dynamically while the bending degrees of freedom are treated adiabatically and one diatom is assumed to be a spectator[12, 13, 14, 15, 16], The RBA may be seen as an extension... 

Abstract. Over the last deeade, advances in quantum dynamics, notably the development of the initial state selected time-dependent wave packet method, coupled with advances in constructing ab initio potential energy surfaces, have made it possible for some four-atom reactions to be addressed from first principles, in their full six internal degrees of freedom. Attempts have been made to extend the time-dependent wave packet method to reactions with more internal degrees of freedom. Here, we review the full-dimensional theory for the A + BCD four-atom reaction and use it to guide the reduced-dimensionality treatment of the X + YCZ3 reaction. Comparison of rigorous calculations with recent experiments are presented for (a) the benchmark H + H2O abstraction reaction, and (b) the H + CH4 H2 + CH3 reaction. 

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