EFFECTS OF REAGENT ROTATION ON THE DYNAMICS OF THE H-2- A FULL DIMENSION QUANTUM STUDY(OH REACTION )

We have extended the time-dependent wave packet method to calculate cr oss sections and rate constants for rotationally excited initial state s by using the centrifugal sudden (CS) approximation. A detailed study of the effects of rotational excitation of reagents on the title reac tion on the WDSE PES has been carried out. It is found that (a) OH rot ational excitation very mildly enhances the total cross section, (b) H -2 rotational excitation quite substantially reduce the cross section, and (c) simultaneous OH and H-2 rotational excitation has a largely u ncorrelated effect. As a result, we found that the thermal rate consta nt can be obtained fairly accurately by only taking into account the e ffect of H-2 rotation. A model calculation by changing the mass of an O atom reveals that the weak dependence of the cross section on OH rot ation is not because the O atom is left relatively stationary by OH ro tation. We speculate that it may be a general feature for the diatom-d iatom reaction that the nonreactive diatom acts as a spectator not onl y vibrationally but also rotationally. It was also found that the ''J- shifting'' approximation works quite well for the reaction. On the oth er hand, the effect of K on the dynamics is found to be much stronger and more complicated than the J effect, making the ''K-shifting'' appr oximation not good for the reaction. (C) 1998 American Institute of Ph ysics.