Polarization-modulated Fourier transform infrared reflection absorption spectroscopy (FT-IRRAS) is used to study the interface between polycrystalline gold electrodes and 0.5 M K2SO4 solution as a function of potential and CN- concentration. Surface cyanide species, adsorbed on the gold electrode, give rise to a 2105-cm-1 C-N stretching band at -1.0 V (Ag/AgCl) which undergoes a shift of approximately 30 cm-1/V to a higher wavenumber at more positive potentials. The species is identified as linearly adsorbed CN” ions. The Au(CN)2- complex, which gives rise to a C-N stretching vibration at 2146 cm-1, is produced in the solution phase by anodic reaction at approximately -0.7 V (Ag/AgCl) and more positive potentials. The shift with coverage of the C-N stretching mode at -1.0 V (Ag/AgCl) is less than ca. 10 cm-1 from low coverage to saturation coverage. Experiments using isotopic mixtures of 12CN and 13CN show that this shift is due to direct lateral interactions between adsorbed cyanide ions. © 1988, American Chemical Society. All rights reserved.