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A New Method for Performing Polarization Modulation Infrared Reflection-Adsorption Spectroscopy of Surfaces

Volume 63, Number 3 (March 2009) Page 369-372

Schennach, Robert; Hirschmugl, Carol; Gilli, Eduard; Tysoe, Wilfred T.

A new and relatively simple polarization modulation technique is presented and tested that enables the whole spectral range to be detected between 400 and 4000 cm−1. This experiment is conventionally carried out using a photoelastic modulator that modulates incident plane polarized light through 90°. This suffers from the drawback that it enables spectra to be collected only over a relatively narrow spectral range. As an alternative, a polarizer is placed in the beam and oriented at 45° to the sample normal. This produces incident radiation fluxes with identical intensities for both s- and p-polarized light. A second polarizer is then modulated through 90° and the surface spectrum is then extracted in the usual manner from the difference between these signals, normalized to their sum. The method is demonstrated for a self-assembled monolayer of 11-mercapto-undecanoicacid (11-MUA) on gold on mica, and it is shown that, while the resulting spectra are extremely sensitive to optical alignment, the method yields spectra that are in excellent agreement with published data.