Chemisorption and reaction of NH3 on Ni(111)

The chemisorption of ammonia on Ni(111) has been investigated using LEED, thermal desorption, and angle-resolved photoemission. For exposures at 200 deg K, thermal desorption shows a coverage-dependent binding energy associated with dipole--dipole interactions. A (2 x 2) LEED pattern occurs at 2-4 L exposure. Time dependence of the LEED pattern and changes in the thermal desorption induced by the LEED beam indicate that the (2 x 2) pattern is due to a stable intermediate decomposition species. Using synchrotron radiation photoemission all three valence orbitals of ammonia have been observed for the first time. The energies of the ammonia-induced features in the photoemission (--22.0, --11.0 and --6.7 eV below the Fermi energy) and the observed symmetries positively identify the adsorbed species as molecular ammonia. Additional structure observed in the photoemission spectra after electron bombardment is associated with the stable adsorbed intermediate. 16 ref.--AA