Experimental studies of amorphous and polycrystalline ice films using FT-RAIRS

A systematic investigation of amorphous and crystalline vapor deposited ice layers with thickness ranging from less than 100 nm to more than 5 mum has been performed using Fourier transform (FT) reflection-absorption infrared spectroscopy (RAIRS). Al and Au. surfaces were used for the vapor deposition and very similar results were obtained on both. The spectra were recorded both with polarized and nonpolarized radiation and simulated with a simple Fresnel reflection model and empirical optical indices from the literature. Optical effects peculiar to this technique like surface suppression or enhancement of vibrational modes, saturation of intense absorptions, and IR interferences, are found to distort the spectra to a greater or lesser extent over the whole thickness range investigated. The diverse spectral band shapes and intensities are globally well reproduced with the mentioned Fresnel model. Some noteworthy discrepancies are, however, observed in the most intense peaks of the polarized spectra, which are affected by larger distortions. Whenever possible, the present measurements have been compared with published spectra recorded under similar conditions and a good accordance has been found. This comparison and the spectral simulations can reconcile seeming discrepancies in the previous literature data.