Quantum calculation of thermal rate constants for the H + D, reaction

Thermal rate constants for the H + D, 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) 3. 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 ( 199 1) 1, we use the adiabatically adjusted principal axis hyperspherical coordinates of Pack [ Chem. Phys. Lett. 108, 333 ( 1984) ] and a direct product C,, symmetry-adapted discrete variable representation to evaluate the Hamiltonian and flux. The initial representation of the J = 0 Hamiltonian in the p 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 K,, 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, k ‘( 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 k ‘( T). Overall thermal rate constants k( 7) are obtained by summing k ‘( T) over J with the weight of 2J + 1 up to J = 30. The results show good agreement with experiments.