Reflection-absorption infrared spectroscopy (RAIRS) displays complex features arising from the interplay between refraction, absorption within the sample, and interference effects between the multiple reflections at the film-substrate and film-vacuum interfaces. The interpretation of the infrared spectra of amorphous solid water (ASW) film is therefore made all the more challenging as spectral features resulting from trivial optical effects are difficult to distinguish from chemically relevant absorption. These difficulties are compounded by the fact that optical, physical and chemical properties can all be greatly impacted by subtle details in sample preparation protocols and experimental conditions. Efforts towards providing a quantitative interpretation of experimental RAIRS spectra, along with a critical review of the numerous optical parameters that have been reported for nanoporous ASW, will be presented. RAIRS spectra from vapour deposited nanoscopic ASW films in the 650-4000 cm<sup>-1</sup> range are compared and contrasted with theoretical infrared spectra calculated using a classical optics model based on Fresnel equations using published optical constants [i.e., n(w) and k(w)][1–3]. On the one hand, selected optical constants from the literature afford a satisfactory description of most experimental spectral band shapes and intensities affording contributions from optical effects to be distinguished from features arising from excitations of molecular vibrations. However, discrepancies with other published optical constants enables the influence of ASW growth conditions on the reported optical parameters to be inferred paving the way for rigorous study of the impact of deposition parameters on morphological properties of vapour deposited ASW films.<br/><br/>

Reflection-absorption infrared spectroscopy is not only a vibrational spectroscopy: Case of thin amorphous solid water (ASW) films

2019 Fall National Meeting

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