A surface penning ionization study of NH3 on Ni(111)

Surface Penning ionization electron spectroscopy was used to investigate the properties of chemisorbed and condensed multilayers of ammonia on Ni(111). We find that the Penning spectroscopy of chemisorbed ammonia provides similar information to ultraviolet photoelectron spectroscopy: we detect emission from the 3a1 and 1e molecular orbitals of NH3. We also find a new peak which we assign to emission from Ni sites whose local work function differs from that of the clean Ni(111) surface. The Penning spectrum of condensed ammonia layers is similar to that of chemisorbed ammonia, but has higher intensity and different peak intensity ratios. Possible reasons for this behavior are suggested. Penning studies of NH3 adsorbed on a Ni(111) surface precovered with hydrogen or oxygen show that the precoverage does not substantially modify the ammonia spectrum. (orig.)