Quantum calculation of thermal rate constants for the H+D2 reaction

Abstract

Thermal rate constants for the H+D2 reaction on the LSTH potential-energy surface are determined quantum mechanically over T=300–1500 K using the quantum flux–flux autocorrelation function of Miller [J. Chem. Phys. 61, 1823 (1974)]. Following earlier works [T. J. Park and J. C. Light, J. Chem. Phys. 91, 974 (1989); T. J. Park and J. C. Light, ibid. 94, 2946 (1991)], we use the adiabatically adjusted principal axis hyperspherical coordinates of Pack [Chem. Phys. Lett. 108, 333 (1984)] and a direct product C2v symmetry-adapted discrete variable representation to evaluate the Hamiltonian and flux. The initial representation of the J=0 Hamiltonian in the ℒ2 basis of ∼14 000 functions is sequentially diagonalized and truncated to yield ∼600 accurate eigenvalues and eigenvectors for each symmetry species block. The J>0 Hamiltonian is evaluated in the direct product basis of truncated J=0 eigenvectors and parity decoupled Wigner rotation functions. Diagonalization of the J>0 Hamiltonian is performed separately for each KJ block by neglecting Coriolis coupling and approximating K coupling by perturbation. Both eigenvalues and eigenvectors are corrected by the perturbation. Thermal rate constants for each J, kJ(T), are then determined by the flux–flux autocorrelation function considering nuclear spins. Due to the eigenvector corrections, both parity calculations are required to determine kJ(T). Overall thermal rate constants k(T) are obtained by summing kJ(T) over J with the weight of 2J+1 up to J=30. The results show good agreement with experiments.