System-bath decomposition of the reaction path Hamiltonian. II. Rotationally inelastic reactive scattering of H+H₂ in three dimensions

Earlier work of the authors [J. Chem. Phys. 77, 2378 (1982)] has shown how the reaction path Hamiltonian of Miller, Handy, and Adams [J. Chem. Phys. 72, 99 (1980)] can be divided into a "system" of the reaction coordinate and modes strongly coupled to it, plus a "bath" of more weakly coupled modes. Quantum mechanical perturbation theory was used to show how one can combine an exact description of the system dynamics with an approximate (perturbative) treatment of the effect of the bath. The present paper applies this approach to the 3d H+H₂ reaction, where the two collinear degrees of freedom constitute the system, and the two bending modes the bath. Comparison with the accurate scattering calculations of Schatz and Kupermann [J. Chem. Phys. 65, 4668 (1976)] shows it to provide a good description of the coupling between bending (i.e., rotational) and collinear modes.