Adchara Padermshoke

Optical Contact in ATR/FT-IR Spectroscopy

Optical contact between an internal reflection element (IRE) and a sample is crucial for obtaining a good spectrum in an attenuated total reflection (ATR) experiment. When an air gap is present between the IRE and the sample, the spectrum severely deteriorates. Two techniques for determining the goodness of contact are proposed—first, by making a comparison between polarized ATR spectra and, second, by making a comparison between ATR and transmission spectra. When the optical contact is achieved, the normalized p-polarized ATR spectrum is exactly the same as the normalized s-polarized ATR spectrum. Moreover, the ratio between the normalized absorbance measured in the ATR mode and the normalized absorbance measured in the transmission mode equals the ratio between the frequency being considered and the normalization frequency. Theoretical and experimental investigations have been performed in order to verify the proposed techniques.

Novel SiO2-deposited CaF2 substrate for vibrational sum-frequency generation (SFG) measurements of chemisorbed monolayers in an aqueous environment.

A novel SiO2-deposited CaF2 (SiO2/CaF2) substrate for measuring vibrational sum-frequency generation (SFG) spectra of silane-based chemisorbed monolayers in aqueous media has been developed. The substrate is suitable for silanization and transparent over a broad range of the infrared (IR) probe. The present work demonstrates the practical application of the SiO2/CaF2 substrate and, to our knowledge, the first SFG spectrum at the solid/water interface of a silanized monolayer observed over the IR fingerprint region (1780–1400 cm−1) using a back-side probing geometry. This new substrate can be very useful for SFG studies of various chemisorbed organic molecules, particularly biological compounds, in aqueous environments.