Infrared Absorption Spectra of Monohydric Alcohols

FTIR spectra of homologous series of monohydric alcohols which belong to the class of partly ordered liquids were registered. The molecules of monohydric alcohols containing hydroxyl group are able to form hydrogen-bonded clusters in the condensed phase. The existence of clusters is clearly observed from the position and the contour of the stretch OH band in the vibrational spectra of liquid alcohols. In this work, the experimentally registered FTIR spectra of liquid n-alcohols from methanol to decanol are presented as well as the same spectra of methanol, ethanol, propanol, butanol, pentanol, and hexanol in gas phase. 1. Introduction The clustering phenomena and structural peculiarities of partly ordered liquids are of great interest in the scientific community. This interest is even growing in context of recent trends and developments in studies on modern multifunctional materials, heterogeneous systems, and nanotechnologies. Among such partly ordered liquids are monohydric alcohols that usually build broad variety of H-bond aggregates. They are quite simple and convenient models to investigate properties of molecular systems sized over the mesoscopic scale (~1–100？nm). The cause of cluster formation in alcohols is the intermolecular hydrogen bond. The vibrational spectra of liquid alcohols differ from their spectra in gas phase or in matrix by the absence of the vibrational band of free hydroxyl group vibrations. Instead of this, the red-shifted diffuse band, which is usually associated with the presence of molecular aggregations (clustering), is observed. However the mechanism of the diffuse band formation and its structure are still the unsolved problems. The importance of the problems connected with the alcohol clustering and structure and, in particular, with the mechanisms of the diffuse absorption band formation is reflected in the great number of experimental [1–9], theoretical [10–14], and combined works [15–19] published in the recent years. The properties of a great number of partly ordered liquids are determined mainly by the characteristics of the hydrogen bond network. Monohydric alcohols are the convenient objects for the investigation of such intermolecular interaction as hydrogen bond. In this work, we present the experimentally registered FTIR spectra of the homologous series of monohydric alcohols in liquid and gaseous states. 2. Methodology The experimental registration of the presented spectra was made in the laboratory of Fourier transform infrared absorption spectroscopy at the Physics Department of Vilnius University,