ESR Studies of Surface Adsorption and Catalysis under Ultra-High Vacuum Conditions. Final Report

摘要

This project was directed to developing ESR for the study of surface adsorption and catalysis on clean and well-characterized metallic and oxide surfaces under uhv conditions to compare the results of such studies with ''real'' surfaces, which are important in actual catalysis. Time resolution of the order of nanoseconds was to be introduced in the study of catalytic processes by means of Laser Time Resolved Electron-Spin Echo (ESE) Spectroscopy. We conducted an extensive study of the new phenomenon of surface-suppressed ESR (SSESR); in which stable paramagnetic radicals adsorbed on clean Ag or Cu surfaces have their ESR signal suppressed until several layers of molecules effectively insulate subsequent layers from the metal surface. This study employed a combination of uhv-ESR, CREMSEE, and thermal desorption techniques. A tentative model based upon transmission of the effects of the surface conduction band of the metal by the weak exchange forces between the paramagnetic species was suggested. In other work: an extended Hueckel MO analysis of our previous O sub 2 /Ti-vycor study was completed; a new and improved photo-CREMSEE apparatus was completed and utilized; analysis of our motional dynamics study of NO sub 2 on zeolites was carried out; and preliminary efforts directed to developing a photo-induced source of H atoms for Laser Time Resolved ESE experiments were carried out. 54 refs., 30 figs., 6 tabs. (ERA citation 11:011642)