SCANNING-TUNNELING-MICROSCOPY AND INFRARED-SPECTROSCOPY AS COMBINED IN-SITU PROBES OF ELECTROCHEMICAL ADLAYER STRUCTURE - CYANIDE ON PT(111)

The spatial structure of irreversibly adsorbed cyanide adlayers on a Pt (111) electrode is deduced by means of in situ scanning tunneling microscopy (STM) combined with infrared reflection-absorption spectroscopy (IRAS). The latter data suggests atop-like Pt-CN coordination. The STM images display a (2 square-root 3 x 2 square-root 3)R30-degrees - 7CN structure, with cyanides bound in symmetric atop sites surrounded by hexagonal ''clusters'' of CN, likely bound in near-atop sites. This arrangement, stable over the applied potential range -0.5 to 0 V versus SCE, gives way to a (2 x 2) structure and disordered adlayers at lower potentials. These findings are compared with previous structural information deduced from ex situ electron diffraction.