ON THE ENERGY-DEPENDENCE OF THE STERIC EFFECT FOR ATOM-MOLECULE REACTIVE SCATTERING .2. THE REACTION CA(D-1)-]CAF((2)PI)+CH3(CH3F(JKM=111))

The observed increase in the steric effect of the reaction Ca(D-1)+CH3 F(JKM =111) -->CaF((II)-I-2)+CH3 with increasing energy has been tenta tively ascribed to a reorientation of the initially oriented CH3F axis , due to anisotropic long-range forces [M. H. M. Janssen, D. H. Parker , and S. Stolte, J. Phys. Chem. 95, 8142 (1991)]. Here we present ab i nitio calculations and use these to construct a long-range potential. To this potential we fit an isotropic model potential and two anisotro pic model potentials. On the long-range potential and on the model pot entials we perform classical trajectory calculations, and we compare t he two methods presented in the preceding paper [G. C. Groenenboom and A. J. H. M. Meijer, J. Chem. Phys. 101, 7592 (1994)] for the extracti on of the steric effect. We conclude that already the attractive isotr opic model presented in this paper can account for the observed energy dependence of the steric effect for this reaction via a ''trapping'' mechanism. We show that although reorientation is possible, it contrib utes little to the positive energy dependence of the steric effect.