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. e molecules of monohydric alcohols containing hydroxyl group are able to form hydrogen-bonded clusters in the condensed phase. e 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.


Introduction
e clustering phenomena and structural peculiarities of partly ordered liquids are of great interest in the scien-ti�c community.is 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.ey are quite simple and convenient models to investigate properties of molecular systems sized over the mesoscopic scale (∼1-100 nm).e cause of cluster formation in alcohols is the intermolecular hydrogen bond.e 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-shied 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.e importance of the problems connected with the alcohol clustering and structure and, in particular, with the mechanisms of the diffuse absorption band formation is re�ected in the great number of experimental [1][2][3][4][5][6][7][8][9], theoretical [10][11][12][13][14], and combined works [15][16][17][18][19] published in the recent years.e 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.

Methodology
e experimental registration of the presented spectra was made in the laboratory of Fourier transform infrared absorption spectroscopy at the Physics Department of Vilnius University, Lithuania.All spectra were registered using Bruker's FTIR spectrometer VERTEX 70 in the spectral range from 750 to 4000 cm −1 .In order to increase signal-to-noise ratio, each spectrum was taken as an average of 128 scans.Liquidphase samples of the monohydric alcohols with purity >99.9 from Fluka were used as received.Gas-phase samples were obtained by the natural evaporation in vacuum process from the liquid surface.
Spectra of liquid n-alcohols were registered by attenuated total re�ection (ATR) method at the resolution 4 cm −1 .e spectrometer was equipped with liquid-N 2 -cooled mercury cadmium telluride (MCT) detector.Blackman apodi�ation function and �ero �lling 2 were used during processing of interferograms.Single-pass ZnSe ATR crystal was used for capturing of the ATR spectra.Angle of incidence of IR beam was set to 70 degree, what insured total re�ection from ZnSe-alcohol interface for all the title alcohols.Spectra of the alcohols in gaseous state were measured using conventional single-pass 10 cm gas cell equipped with KBr windows with the resolution 0.5 cm −1 using deuterated triglycine sulfate (DTGS) detector.Blackman-Harris 3-term apodi�ation function and �ero �lling 12� were used during processing of interferograms.Pressure of each alcohol was set close to its saturated pressure at 20 ∘ C: 13 mbar for methanol, 5.5 mbar for ethanol, 2 mbar for 1-propanol, 0.7 mbar for 1butanol, 0.2 mbar for 1-pentanol, and 0.1 mbar for 1-hexanol.
e gas cell was �lled with an alcohol using standard vacuum technique.Atmospheric oxygen and nitrogen were removed from the alcohols by �ve free�e-pump-thaw cycles.

Dataset Description
e dataset associated with this Dataset Paper consists of 16 items which are described as follows.
Dataset Item 1 (Spectrum).FTIR spectrum of liquid methanol CH 3 OH (Figure 1).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).
Dataset Item 2 (Spectrum).FTIR spectrum of liquid ethanol C 2 H 5 OH (Figure 2).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).Dataset Item 3 (Spectrum).FTIR spectrum of liquid propanol C 3 H 7 OH (Figure 3).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).
Dataset Item 4 (Spectrum).FTIR spectrum of liquid butanol C 4 H 9 OH (Figure 4).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).
Dataset Item 5 (Spectrum).FTIR spectrum of liquid pentanol C 5 H 11 OH (Figure 5).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).Dataset Item 6 (Spectrum).FTIR spectrum of liquid hexanol C 6 H 13 OH (Figure 6).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).
Dataset Item 7 (Spectrum).FTIR spectrum of liquid heptanol C 7 H 15 OH (Figure 7).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).
Dataset Item 8 (Spectrum).FTIR spectrum of liquid octanol C 8 H 17 OH (Figure 8).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).F 12: FTIR spectrum of gaseous ethanol.
Dataset Item 9 (Spectrum).FTIR spectrum of liquid nonanol C 9 H 519 H (Figure 9).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).
Dataset Item 10 (Spectrum).FTIR spectrum of liquid decanol C 10 H 21 OH (Figure 10).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).
Dataset Item 11 (Spectrum).FTIR spectrum of gaseous methanol CH 3 OH (Figure 11).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).F 14: FTIR spectrum of gaseous butanol.
Dataset Item 12 (Spectrum).FTIR spectrum of gaseous ethanol C 2 H 5 OH (Figure 12).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).
Dataset Item 13 (Spectrum).FTIR spectrum of gaseous propanol C 3 H 7 OH (Figure 13).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).
Dataset Item 14 (Spectrum).FTIR spectrum of gaseous butanol C 4 H 9 OH (Figure 14).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).
Dataset Item 15 (Spectrum).FTIR spectrum of gaseous pentanol C 5 H 11 OH (Figure 15).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).
Dataset Item 16 (Spectrum).FTIR spectrum of gaseous hexanol C 6 H 13 OH (Figure 16).FTIR spectrum is the dependence of the infrared absorbance (measured in arbitrary units (a.u.)) on the wavenumber (measured in the reversed centimeters (cm −1 )).

Concluding Remarks
In this work, the experimentally registered IR absorption spectra of monohydric alcohols in liquid and gaseous state are presented.e collected experimental data can be useful for the investigations of the structure and properties of partly ordered liquids, dynamics and kinetics of cluster formation processes in hydrogen-bonded systems, peculiarities of phase transitions from gas to liquid in such objects, and so forth.
F 6: FTIR spectrum of liquid hexanol C 6 H 13 OH.
F 8: FTIR spectrum of liquid octanol C 8 H 17 OH.