Reactive scattering, atom-diatom approach

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. 

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

Thus, the critical measure of the applicability of a method to polyatomic reaction dynamics is the scaling of its computational cost with respect to the number of basis functions or degrees of freedom. Since the standard time-independent scattering methods solve boundary-value problems, they scale as with the number of basis functions N, and are thus difficult to extend to large systems. Until a few years ago, the reduced-dimensionality approach (RDA) [32, 33] provided the only means for treating the four-atom reactive scattering problem in which a four-atom reaction system is reduced to an effective atom-diatom system through the elimi-... 

ABSTRACT. In this paper, the theoretical basis and the program architecture of some reduced dimensionality quantum reactive scattering computational procedures are illustrated. The aim is to evidence to what extent it is possible to take advantage of parallel and vector performances of modem supercomputers for carrying out extensive calculations of the reactive properties of atom diatom systems. Some efforts have been paid to indicate alternative ways of formulating both the theoretical approaches and the computational codes. Speed-up factors of the suggested solutions have been calculated for some test cases. Results of extensive calculations performed for two prototype reactive systems are presented. 

The ABC approach to quantum reactive scattering was originally derived to compute the cumulative reaction probability [26, 27]. It was then applied to the calculation of initial state selected and state-to-state reaction probabilities [28]. Thorough discussions of the theory can be found in these references. For completeness, a brief outline of tne formulae relevant for atom-diatom reactions is provided below. 

Rotating bond approximation calculations as applied to the CH4 + OH CH3 + H2O reaction have been discussed. The scattering calculations are performed within a model which treats CH3 as a pseudo-atom and CH4 as a pseudo-diatom. The rotation of OH, a reactive C-H stretch of CH4, two vibrations of H2O and relative translation are treated explicitly in the scattering calculations. An adiabatic approach is used to account for all other degrees of freedom. The reduced dimensionality potential energy surface RDPl [17] was employed in the calculations. 

---