Ammonia adsorption on the Ag(110) surface

Abstract

Adsorption of ammonia on the Ag(110) surface has been studied by thermal desorption spectroscopy and electron energy loss spectroscopy. Ammonia adsorbs in molecular form; no dissociation was observed by thermal desorption or vibrational spectroscopy. Three desorption peaks were observed and were correlated with vibrational spectra. Chemisorbed ammonia desorbs in a broad peak in the 145 to 210 K temperature range. Comparison of vibrational and desorption results with similar data from the Pt(111) surface [1–4] indicates that chemisorbed ammonia is adsorbed by charge transfer from the nitrogen lone pair into the metal surface. The second layer of ammonia hydrogen bonds to the chemisorbed ammonia and desorbs at 122 K. Sublimation of solid ammonia occurs at 109 K. In all three states the vibrational transitions of ammonia occur at the same energies as the vibrational transitions of solid ammonia indicating no significant perturbation of molecular geometry. The smaller adsorption strength for ammonia chemisorbed on silver relative to ammonia adsorbed on platinum suggests that the work function (electron affinity) may be a primary factor which influences charge transfer bonding.