Cluster KN formation by Rydberg collision complex stabilization during scattering of a K beam off zirconia surfaces

Abstract

The molecular beam scattering of a K atom beam off a zirconia surface at 1100 K is studied with four different detection techniques: field ionization, which is sensitive only to field ionizable Rydberg species, in this case, with principal quantum number n>29; ion collection, which is sensitive only to positive ions; ion multiplier detection, which will give a response for both positive ions and Rydberg species; and finally, surface ionization detection, which will give a signal proportional to the flux of all forms of K, including excited K* species and clusters KN. Combining all these methods, the different scattering processes can be disentangled. A condensation scattering process is observed between a K beam atom and an electronically excited cluster KN* at the surface. This is seen in the angular distributions as several sharp peaks in the angular directions of the center-of-mass motion for the complexes formed. Electronically excited species K* and KN* are formed by thermal excitation due to mechanisms which have recently been investigated in detail for the K–graphite surface interaction. Electronically excited clusters KN* with N at least up to 4 exist at the surface. Specular scattering is observed, which indicates an excitation energy exchange and scattering of a K* atom in a repulsive state interaction with the surface. Backwards ion formation scattering is also observed, due to cluster decomposition. The processes giving scattering of excited species are very sensitive to the external electric-field strength.