THE CUMULATIVE REACTION PROBABILITY FOR THE H-2+OH REACTION

The cumulative reaction probability [CRP or N(E)] for the four-atom re action, H-2+OH-->H +H2O is calculated using one of the formulations of Miller, Schwartz, and Tromp [J. Chem. Phys. 79, 4889 (1983)] and the transition state wave packet (TSWP) approach of Zhang and Light [J. Ch em. Phys. 104, 6184 (1996)]. It is shown that locating the dividing su rface of the flux operator in the transition state region significantl y reduces the number of wave packets which must be followed in order t o converge the CRP as compared to the use of initial state selected wa ve packets (ISSWP). In addition we examine the use of transition state normal coordinates (versus Jacobi coordinates) and show that the use of transition state wave packets defined in normal coordinates yields more rapid convergence of the CRP and individual contributions of the TSWP to the CRP can closely approximate the probabilities of reaction for each transition state as a function of energy. Problems with large amplitude motions using the normal coordinates of the loose non-linea r transition state are shown to be absent if normal coordinates of a l inear transition state are used. Applications to the 3-D H + H-2 (J = 0) reaction and to the 6D H-2 + OH (J = 0) reaction demonstrate that b oth N(E) and the initial state reaction probabilities at many energies can be evaluated accurately and efficiently by propagation of each TS WP only once. (C) 1997 American Institute of Physics.