Adsorption of 4-cyanopyridine on Au(111): ab initio calculations and SFG measurements

The adsorption of 4-cyanopyridine (4-CP) on a gold single crystal electrode in sodium perchlorate supporting electrolyte has been investigated by volt ammetry, sum frequency generation (SFG) and ab initio calculations. Combina tion of in situ vibrational SFG spectra and DFT, MP2 and MP2 + SQM calculat ions allows us to obtain fundamental information on the behavior of adsorbe d 4-CP as a function of the electrode potential. The configuration of the a dsorbed 4-CP is dependent on the electrode potential. 4-CP is adsorbed perp endicular to the electrode surface through the pyridine nitrogen at negativ e potential, and through the nitrile nitrogen at positive potential. In the intermediate potential range, the molecule is adsorbed parallel to the ele ctrode surface, through the pi electrons of the aromatic ring.