ANGULAR AND VELOCITY DISTRIBUTIONS OF CO DESORBED FROM ADSORPTION LAYERS ON NI(100) AND PT(111) - EXAMPLES OF NONACTIVATED DESORPTION

Angular and velocity distributions of Co thermally desorbing from Ni(1 00) and Pt(III) have been measured in a time-of-flight experiment. Cov erages were averaged over ranges with approximately constant desorptio n parameters. In all cases, independent of coverage, an angular depend ence approximately cos(theta) was found up to desorption angles of 85- degrees. Desorption fluxes are excellently described by Maxwellian vel ocity distributions. The average kinetic energy of desorption, however , deviates significantly from 2kT(s) (where T(s) is the mean surface t emperature). The values measured vary between 1.88kT(s) and 1.91kT(s). Where checked (Pt) no dependence on coverage was found. This result o f slight translational cooling has to be expected both from theory for this class of systems as well as from sticking measurements via detai led balance.