A SNIFTIRS study of the adsorption of pyridine at the Au(111) electrode-solution interface

Subtractively normalized interfacial Fourier transform infrared spectroscopy (SNIFTIRS) has been applied to study coordination of the pyridine molecules to the Au(lll) electrode surface. The IR spectra have been recorded using both p- and s-polarized radiation. The ratio of the integrated band intensities for the spectra recorded with p- and s-polarized light was then used to study changes in the surface coordination of pyridine molecules. We have derived an expression describing the dependence of this ratio on the tilt angle. We have described the orientation of the adsorbed molecule in terms of angles formed between the surface, and: (i) C-2 nu axis of the pyridine molecule, (ii) the direction in plane of the molecule and normal to the C-2 nu axis. We were able to demonstrate that both angles increase by moving from negative to positive potentials. This result indicates that the pyridine molecule not only stands up at positive potentials but also its plane rotates somewhat with respect to the electrode surface. (C) 1999 Elsevier Science Ltd. All rights reserved.