We develop a wave packet approach to treating the electronically nonadiabat
ic reaction dynamics of O(D-1) + H-2 --> OH + H, allowing for the 1(1)A' an
d 2(1)A' potential energy surfaces and couplings, as well as the three inte
rnal nuclear coordinates. Two different systems of coupled potential energy
surfaces are considered, a semiempirical diatomics-in-molecules (DIM) syst
em due to Kuntz, Niefer, and Sloan, and a recently developed ab initio syst
em due to Dobbyn and Knowles (DK). Nonadiabatic quantum results, with total
angular momentum J = 0, are obtained and discussed. Several single surface
calculations are carried out for comparison with the nonadiabatic results.
Comparisons with trajectory surface hopping (TSH) calculations, and with a
pproximate quantum calculations, are also included. The electrostatic coupl
ing produces strong interactions between the 1(1)A' and 21A' states at shor
t range (where these states have a conical intersection) and weak but, inte
restingly, nonnegligible interactions between these states at longer range.
Our wave packet results show that if the initial state is chosen to be eff
ectively the 1A' state (for which insertion to form products occurs on the
adiabatic surface), then there is very little difference between the adiaba
tic and coupled surface results. In either case the reaction probability is
a relatively flat function of energy, except for resonant oscillations. Ho
wever, the 2A' reaction, dynamics (which involves a collinear transition st
ate) is strongly perturbed by nonadiabatic effects in two distinct ways. At
energies above the transition state barrier, the diabatic limit is dominan
t, and the 2A' reaction probability is similar to that for 1A ", which has
no coupling with the other surfaces. At energies below the barrier, we find
a significant component of the reaction probability from long range electr
onic coupling that effectively allows the wave packet to avoid having to tu
nnel through the barrier. This effect, which is observed on both the DIM an
d DK surfaces, is estimated to cause a 10% contribution to the room tempera
ture rate constant from nonadiabatic effects. Similar results are obtained
from the TSH and approximate quantum calculations.