MOLECULAR-BEAM EXPERIMENT FOR ADSORPTION-KINETICS AND CATALYTIC REACTIONS STUDIES

An ultrahigh-vacuum apparatus has been designed to study the chemisorption of molecules on surfaces, as well as chemical reactions catalyzed on small metal particles, by molecular-beam techniques. Two beams of reactant molecules threefold differentially pumped can be aimed onto the sample surface under variable angle of incidence. A mass spectrometer, located at a variable distance from the sample in a separate chamber, detects molecules which have left the surface after interaction. Auger electron and x-ray photoelectron spectroscopies can be used to characterize the sample. The drift time froin the source to the detector has been calibrated using supersonic pulsed beams of rare gases; the time resolution of the experiment is about 2-mu-s. Measurements of the adsorption of CO on Pt(111) and Pt(997) surfaces have been performed. First results using the pulsed beam technique on both surfaces are presented along with results obtained from the Pt(111) surface by thermal helium beam scattering.