Vibrational spectra of hydrogen on the Rh(111) surface

High resolution electron energy loss spectra of H(D) on Rh(lll) at 90 K hav e been studied in detail. Losses are observed at 79-90 (60-67) and similar to 135 (98) meV, which are attributed to the asymmetric and symmetric stret ching modes of H(D) atoms in the threefold hollow sites, respectively. The 79-90 (60-67) meV loss is anomalously broad and the intrinsic width is 15-2 4(10-14)meV. The origins of loss peak width and loss energy shift are discu ssed. No evidence of the quantum delocalization of the adsorbed H was found in contradiction to the work previously reported by another group. (C) 199 9 Elsevier Science B.V. All rights reserved.