COLLISIONS OF NO(CHI-2-PI) WITH A AG(111) SURFACE - NEW QUANTUM SCATTERING STUDIES BASED ON A SEMIEMPIRICAL POTENTIAL-ENERGY SURFACE

We report the results of fully quantum close-coupled studies of collisions of NO(X2-PI) with a Ag(111) surface. The recent corrected effective medium potential energy surfaces (PES) of DePristo and Alexander [J. Chem. Phys. 94, 8454 (1991)] were used. The final state rotational distributions show evidence of at least four rotational rainbows, corresponding to scattering on (and interference between) the two PES which arise when the degeneracy of the NO molecule is lifted upon approach to the surface. A strong tendency is seen to populate the lower spin-orbit manifold at low to moderate final J, which disappears as J rises beyond 30.5 and the final states are better described in Hund's case (b). Simultaneously, there exists a propensity to populate those A-doublet levels in which the electronic-rotational wave function is antisymmetric (PI-A") with respect to reflection of the electronic coordinates in the plane of rotation of the scattered NO molecule. This feature is opposite to what has been seen experimentally. An approximate averaging over the lateral position of the NO molecule above the surface showed that although the rainbow oscillations are strongly sensitive to surface corrugation, the fine-structure propensities are not. This suggests that these latter are reflective of some fundamental characteristic of the NO-Ag interaction which is independent of the position of the NO molecule above the Ag(111) unit cell.