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

Abstract

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.

In situ PM-IRRAS of a glassy carbon electrode/deep eutectic solvent interface

“…In addition, the geometry of the two polarisers ensures a constant intensity in s and p. A detailed description of the method has been published by Schennach et al 37 All spectra were collected at 4 cm À1 spectral resolution using 200 scans and are presented without smoothing. The light beam was incident at 701 with respect to the surface normal onto the sample and the light was detected by a liquid nitrogen-cooled mercury cadmium telluride detector.…”

“…54 Additionally, the electrode must be highly reflective to the IR radiation. 37 It is important to remark that within the electrolyte layer the intensity of s-and p-polarized light might not be the same. 33 For each measurement, a p-and a s-polarized spectrum has been obtained.…”

“…26 Differences for the IR bands of bulk and thin film spectra arising from the substrate-IL interactions at open circuit potential were reported. 37 The difference between the p-and s-polarized spectra divided by the sum of the two yields an IR spectrum of the surface species. Thus, the s-spectrum can be used as a background.…”

Determination of Noise-Free Optical Constants in the Infrared by Kramers—Kronig Transformation of the Reflectance Ratio in s- and p-Polarization

“…The experiments were carried out on a Bruker ifs 66v/s vacuum Fourier Transform Infrared (FT-IR) Spectrometer with a Bruker A 513 variable angle specular reflection accessory. For a constant background in the s-and p-directions, a two polarizer method 30 was chosen, where the first polarizer is set to a polarization angle of 458 between the s-and p-directions. To get rid of time-dependent drifts of the spectrometer (especially in the region of water absorption), the measurement was carried out with an automatization macro that switches the angle of the second polarizer between the s-and p-direction repeatedly and yields the averaged s-and p-spectra.…”

“…To get rid of time-dependent drifts of the spectrometer (especially in the region of water absorption), the measurement was carried out with an automatization macro that switches the angle of the second polarizer between the s-and p-direction repeatedly and yields the averaged s-and p-spectra. 30 For a single measurement, 200 scans were recorded at a mirror velocity of 100 kHz. The measurements were repeated 80 times and the resulting mean spectra were used as reflectance data.…”