QUANTUM CALCULATIONS ON THE ADSORPTION OF HALIDE-IONS ON THE NOBLE-METALS

The interaction of halide ions with the three noble metals has been in vestigated using the B3LYP density functional method and the cluster m odel approximation. The results of calculations for the M-X- and M-12- X- (M = Cu, Ag, Au; X = F, Cl, Br, I) systems are presented. At the (1 00) surface, modeled in the present work by the M-12 cluster, all hali de ions have been found to adsorb preferentially at the hollow site, f ollowed by the bridge and by the top positions, The adsorption energy has been found to decrease when going from fluoride to iodide in both atom-ion and cluster-ion cases. The opposite trend is observed for the estimates of the charge transfer from the ions to the surface. When d ifferent metals are compared, the M12X- interaction energies decrease in the order Au > Ag > Cu, but for the smaller ions some deviations fr om this line do appear, The relative values of the calculated harmonic vibrational frequencies do agree with those found experimentally, but their magnitude is much smaller as a result of the effect of the lowe r surface coverage.