ELSEVIER Surface Science 339 (1995) 329-336 iiiiiiiiiiii•iiiiii••iii•i•iiiiiiii!i•iiiii!iiiiiiiiiiii•iiiii••ii••ii•ii•iiiiiiiiiiiii surface science Linear polarization discrimination for in situ infrared spectroscopy at electrode surfaces Peter W. Faguy *, Nebojsa S. Marinkovic 1 Department of Chemistry, University of Louisville, Louisville, KY40292, USA Received 29 March 1995; accepted for publication 19 May 1995 Abstract Linear polarization absorption ratios are determined from data for carbon monoxide and bisulfate anion adsorbed on Pt single crystal electrodes and are compared to the extinction coefficient for the wire grid polarizer utilized. The two adsorbates are at sub-monolayer coverages and have dipole moments, for the IR modes observed, which are normal to the electrode surface. Thus their intensities provide a direct measure of the available parallel polarized light intensity regardless of the actual linear polarization state selected. From the relative absorption ratios it is apparent that the linear polarization discrimination is much less than the predicted values from the polarizer extinction coefficients. The decrease in extinction efficiency for the in situ measurement as compared to the polarizer response is explained in terms of the polarization rotation at the window/solution/electrode interface and the relative linear polarization throughput for the spectrometer. Keywords: Chemisorption; Infrared absorption spectroscopy; Low index single crystal surfaces; Metal-electrolyte interfaces; Platinum; Reflection spectroscopy;Vibrations of adsorbed molecules 1. Introduction The application of infrared spectroscopy to prob- lems of molecular structure at electrode surfaces is arguably the most useful and versatile hybrid spec- troelectrochemical technique in use today. Informa- tion concerning the coverage, structure and orienta- tion of molecular species on electrode surfaces as well as the concentration near the electrode can be obtained [1,2]. The reflection techniques involved utilizes difference in absorption for orthogonally lin- * Corresponding author. Fax: + 1 502 852 8149. Present address: Department of Chemistry, Universityof Cali- fornia, Davis, USA. early polarized radiation [3,4]. Differences in parallel (p-) and perpendicular (s-) mean square electric field strengths (MSEFS) exist because of the boundary conditions found for electromagnetic fields at a con- ductor/dielectric interface [3-7]. This provides the surface sensitivity inherent to near-grazing angle ex- ternal [3,4] and critical angle internal [8-10] reflec- tion techniques. Signal enhancement in the form of large MSEFS for the parallel polarized light, and signal discrimination as the rejection of the perpen- dicularly polarized component to increase signal at the detector, both are operative in linear polarized surface reflection spectroscopy. These concepts are well established and many of the interpretive and sensitivity considerations can be found in the litera- ture [1-12]. 0039-6028/95/$09.50 © 1995 Elsevier Science B.V. All rights reserved SSD1 0039-6028(95)00671-0