Vibrational frequencies of halogen atoms adsorbed on silver metal surfaces

The vibrational frequencies of halogens adsorbed on Ag(100) are calculated. The frequency of a single adsorbed atom vibration perpendicular to the surface is obtained from AgX (X=F, Cl, Br, I) crystal frequencies. Interaction between dipoles consisting of the effective charge on the adsorbed atom and its induced image charge produces a coverage dependent frequency. The effective charge on the adsorbed atom is assumed to be 1.0e, while the electronic polarizability of the real-plus-image atom system is assumed to be twice the electronic polarizability of X−. At full coverage, the calculated frequencies for the k=0 modes are 437, 241, 150, and 113 cm−1, respectively, for X=F, Cl, Br, I, which compare well with experimental values, and these frequencies are assigned to external vibrational model of halogen atoms adsorbed on silver.