The e β ects of electron impact on ammonia-covered Pt(111) have been studied using temperature-programmed desorption (TPD) and electron-stimulated desorption (ESD). For coverages below one monolayer, ammonia adsorbs on the surface in two distinct TPD states : the a-state is broad and desorbs over the temperature range 150-350 K, and the b-state appears as a sharper peak at 150 K. The b-state was seen to be damaged by electronbeam impact much more readily than the a-state, resulting in the formation of atomically adsorbed N on the surface. The mass 28 recombinative nitrogen desorption TPD peak appearing at 550 K exhibited second-order desorption kinetics, further conΓrming the presence of atomically adsorbed nitrogen. The ESD kinetic energy distributions (KEDs) were obtained for m/e = 1 amu, which exhibited broad peaks generally. The H' KEDs were analyzed using empirical curve Γts, with the resulting conclusion that the H' KEDs contain contributions from at least three di β erent hydrogen-containing surface species. We believe that these three H' KED peaks are due to ESD from adsorbed and H. The ESD cross-section for removal was measured in three di β erent NH 3 , NH 2 NH 3 ways, all of which were found to be in general agreement, and which gave an averaged cross-section value of cm2.
1998 John Wiley & Sons, Ltd. Q tot = 4 Γ 10-17