CYANIDE ADSORBED ON COINAGE METAL-ELECTRODES - A RELATIVISTIC DENSITY-FUNCTIONAL INVESTIGATION

The adsorptive properties of cyanide (CN-) on coinage metal (M) electr odes (M = Cu, Ag, Au) have been investigated using a relativistic dens ity functional method. The way to model the electrochemical potential applied to the electrodes is to consider the systems in the presence o f a perturbative external field F. The field-perturbative approach is proven to be a suitable method in interpreting the observed spectral s hifts with electrode potential. The calculated potential-dependent shi fts of omega(M-CN) and omega(C-M) are similar for the three metals, in agreement with experiment observations. The relativistic effects are required to account for the similarity in the frequency shifts of omeg a(M-CN). The calculated vibrational tuning rates d omega(C-N)/dF are 6 .61 x 10(-7), 6.61 x 10(-7), and 5.64 x 10(-7) cm(-1)/(V/cm) for M = C u, Ag, and Au, respectively. The coupling of the M-CN and C-N internal modes contributes significantly (about 25%) to the size of the freque ncy shifts Delta omega(C-N) of the ligand. The effect of electric fiel ds on the metal-CN- bonding is also investigated. It is shown that cha nges in the magnitude of CN- to the metal donation and M-CN bond stren gth occur under the influence of the electric field. (C) 1998 John Wil ey & Sons, Inc.