IR spectroscopy of ethanol in nitrogen cryomatrices with different concentration ratios

Abstract

Thin films of cryovacuum condensates of ethanol-nitrogen mixtures formed by co-condensation of gas mixtures with different concentrations on a cooled metal substrate are studied by IR spectrometry. The condensation temperature was Tc = 16 K and the pressure of the gaseous phase during cryodeposition was P = 10−5 Torr. The ethanol concentration in nitrogen was varied from 0.5 to 10% and the film thickness, from 1 to 30 μm. Measurements were made in the range from 400 to 4200 cm−1. An analysis of the IR spectra and a comparison with published data shows that ethanol monomers and dimers are present in the nitrogen matrix. This is indicated by an absorption band at a frequency of 3658 cm−1 owing to vibrations of O–H bonds of ethanol monomers and dimers. The local minima of this band at 3645 and 3658 cm−1 are related to the existence of two conformational states of the ethanol molecule: anti (3658 cm−1) and gauche (3645 cm−1). In addition, the presence of ethanol dimers and monomers in the matrix leads to the appearance of absorption bands at 1259 and 1276 cm−1 attributable to deformation vibrations δ(COH) of the anti- and gauche-isomers, respectively, as well as bands corresponding to a combination of ν(CCO) valence vibrations and rotational oscillations of the methyl group r(CH3) attributable to anti-dimers (ν = 1090 cm−1) and anti-monomers (ν = 1095 cm−1). Local minima within 3000–3600 cm−1 also indicate the presence of cyclical dimers, trimers, and tetramers, as well as hexamers in the matrix. A broad band over 3250–3330 cm−1 indicates that large polyaggregates, with ethanol molecules in a hydrogen-bond state (multimer), exist in the matrix.