Assignment of the vibrational features in the Rh(1 1 1)–(2×2)-3CO adsorption structure using density functional theory calculations

Calculated CO stretching frequencies for the Rh(1 1 1)–(2×2)-3CO structure are compared with recent high-resolution electron energy loss spectroscopy (HREELS) experiments. Two loss peaks in the HREELS spectrum at 2070 and 1861 cm−1 were attributed to ontop- and hollow-bonded CO molecules, respectively. Two weaker peaks, which had not been observed before due to the lack of resolution, appeared at 1785 and 1925 cm−1. DFT calculations reveal that the loss features at 1861 and 1785 cm−1 originate from the adsorption of CO molecules at hcp and fcc sites and correspond to the in-phase and out-of-phase normal modes resulting from dipole–dipole coupling.