COLLISION DYNAMICS OF ALKALI-METAL ATOMS WITH ORIENTED SYMMETRICAL-TOP MOLECULES

Theoretical calculations based on the long-range dynamics of the harpoon model have been used to predict the effects of reactant orientation upon ionization yields and angular distributions of product MX for reactions of alkali-metal atoms M with oriented symmetric-top molecules of general formula CY3X, where X is a halogen and Y is H, F, or methyl. Large effects of orientation upon ionization yield near threshold are found to result from differences in the partitioning of kinetic energy between relative motion and center-of-mass motion, depending on whether the X- ion ejected by the unstable CY3X- ion is traveling in the same direction as the incoming M+ ion or the opposite direction. For most systems for which comparison is possible, excellent agreement is obtained with experimental data on the effect of orientation upon ionization yield. For ionizing collisions of fast K atoms with CH3I and CH3F, and for product angular distributions found with thermal K atoms and oriented CF3I and CF3Br, the theory is less successful and it appears that orientation-dependent short-range interactions must play a major role.