Recrossing effects

While the quantum instanton approximation cannot describe the recrossing effect, this effect, which is predominantly classical, could be included empirically as a multiplicative factor (a transmission coefficient ) obtained in a classical molecular dynamics simulation. The main challenge for future research is to develop accurate and efficient approximations for the rate constant, its temperature dependence, and the kinetic isotope effect that include the quantum and recrossing effects simultaneously and rigorously. 

For most realistic systems, the recrossing effect of the ET reaction can be neglected, i.e. k(/) = 1. In such a case, krsr itself should predict a reasonable ET rate. However, when the transferred electron in the acceptor state has not enough time to relax its energy to the environment, the electron can recross to the donor state. In this energy diffusion limit, the dynamic transmission... 

As we go to the right in the above sequence, the methods accoiuit more accurately for recrossing effects. 

The only quantum calculations thus far on 0 + H2 are collinear ones reported in reference 96 for the JW and SL surfaces and in the chapter by Bowman and Lee in this book for the DIM and POLCI-RMOS surfaces. These are all single-surface ( A") calculations. The results on the DIM surface tend to reaffirm our statement above concerning recrossing effects. Presumably a multiple-surface quantum treatment of 0 4- H2 in three dimensions is well into the future. 

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