Applications of Quantitative SNIFTIRS

Quantitative SNIFTIRS was introduced in 2002 and so far has been applied to the investigation of the orientation of adsorbed molecules in three systems pyridine at Au(llO) [40], citrate at Au(lll) [53], and 2-mercaptobenzimidazole at Au(lll) [54, 55]. Pyridine adsorption at gold single-crystal surfaces has long been used as a model system to study the coordination of organic molecules to metal electrode surfaces. The thermodynamics of pyridine adsorption has been thoroughly investigated with the help of the chronocoulometric technique [56-64]. The availability of the thermodynamic data made this an ideal system to test the performance of the quantitative SNIFTIRS. 

In the plateau region, the coverage of the electrode surface by adsorbed molecules is constant However, the static electric field at the interface changes sig- 

At this point one performs a second calculation of a hypothetical film of randomly oriented pyridine molecules 1 — f mstrix method is used 

The studies of 2-mercaptobenzimidazole (MBI) adsorption at an Au(lll) electrode surface [54, 55] constitute the third example of quantitative analysis of SNIFTIRS spectra being employed to reveal the orientation of an adsorbed molecule. The inset to Fig. 9.25 shows that the transition dipoles of the Ai bands are directed along the C2 axis of the MBI molecule. Hence, quantitative analysis of these bands allows one to determine the tilt of this axis with respect to the surface normal. The angle 9, determined from quantitative analysis of SNIFTIRS spectra, is plotted as a function of the electrode potential in Fig. 9.25. This angle is relatively large, but its value progressively decreases when the potential is changed in the positive direction. The SNIFTIRS spectra also showed that the intensity of B2 bands for adsorbed molecules is very weak, and hence their transition dipoles (in the plane of the molecule and perpendicular to the C2 axis) are essentially perpendicular to the surface normal. 

In conclusion, quantitative SNIFTIRS is a powerful technique for studying the orientation of organic molecules at electrode surfaces. It works best when 

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