Quantum and quasiclassical studies of the O(P-3)+HCl -> OH+Cl(P-2) reaction using benchmark potential surfaces

We have performed quantum mechanical (QM) dynamics calculations within the independent-state approximation with new benchmark triplet A(') and A(') surfaces [B. Ramachandran , J. Chem. Phys. 119, 9590 (2003)] for the rovibronic state-to-state measurements of the reaction O(P-3)+HCl(v=2,j=1,6,9)-->OH(v(')j('))+Cl(P-2) [Zhang , J. Chem. Phys. 94, 2704 (1991)]. The QM and experimental rotational distributions peak at similar OH(j(')) levels, but the QM distributions are significantly narrower than the measurements and previous quasiclassical dynamics studies. The OH(low j(')) populations observed in the measurements are nearly absent in the QM results. We have also performed quasiclassical trajectory with histogram binning (QCT-HB) calculations on these same benchmark surfaces. The QCT-HB rotational distributions, which are qualitatively consistent with measurements and classical dynamics studies using other surfaces, are much broader than the QM results. Application of a Gaussian binning correction (QCT-GB) dramatically narrows and shifts the QCT-HB rotational distributions to be in very good agreement with the QM results. The large QCT-GB correction stems from the special shape of the joint distribution of the classical rotational/vibrational action of OH products. We have also performed QM and QCT calculations for the transition, O+HCl(v=0,T=300 K)-->OH(v(')j('))+Cl from threshold to similar to130 kcal mol(-1) collision energy as a guide for possible future hyperthermal O-atom measurements. We find in general a mixed energy release into translation and rotation consistent with a late barrier to reaction. Angular distributions at high collision energy are forward peaked, consistent with a stripping mechanism. Direct collisional excitation channel cross sections, O+HCl(v=0,T=300 K)-->O+HCl(v(')=1), in the same energy range are large, comparable in magnitude to the reactive channel cross sections. Although the (3)A(') state dominates most collision processes, above similar to48 kcal mol(-1), the (3)A(') state plays the major role in collisional excitation. (C) 2005 American Institute of Physics.