From clusters to condensed phase – FT IR studies of water V. Pogorelov a, ⁎, I. Doroshenko a , G. Pitsevich b , V. Balevicius c , V. Sablinskas c , B. Krivenko a , L.G.M. Pettersson d a Taras Shevchenko National University of Kyiv, Volodymyrska str., 64\13, 01601 Kyiv, Ukraine b Vilnius University, Sauletekio 9-3, LT-10222 Vilnius, Lithuania c Belarusian State University, Nezavisimosti ave., 4, 220030 Minsk, Belarus d AlbaNova University center, Stockholm University, SE-10691 Stockholm, Sweden abstract article info Article history: Received 12 September 2016 Received in revised form 30 November 2016 Accepted 5 December 2016 Available online xxxx Intermolecular hydrogen bonding, which is formed between water molecules in the condensed state, causes a variety of unique properties of liquid water. In this paper the results of experimental FT IR studies of water trapped in an Ar matrix as well as condensed water at temperatures from 133 to 293 K are presented. It is shown that the temperature evolution of the FTIR-spectra of water trapped in low-temperature matrices can be considered as an experimental model of the structure transformation of water during the phase transition from gas phase to condensed confined water. The comparison of the vibrational spectra of water in matrix isola- tion with the corresponding spectra of condensed water gives information about the peculiarities of H-bonded structures of water. © 2016 Elsevier B.V. All rights reserved. Keywords: Water Cluster FTIR Matrix isolation Hydrogen bond 1. Introduction Water is the most important liquid on our planet and it is also one of the most anomalous with many properties that deviate from those of other liquids [1], so it is not surprising that it has been intensively stud- ied by various methods. In recent years, several reviews have been de- voted to different aspects of water [2–6] devoted to experimental and theoretical investigations of water structure and properties. Of particu- lar interest in connection with the present work is the large number of experimental studies using infrared spectroscopy and matrix isolation techniques to determine properties of small aggregates of water mole- cules [7–19], Intermolecular hydrogen bonding, which is formed be- tween water molecules, causes a variety of unique properties of this liquid. These anomalous properties of water were studied both by ex- perimental and theoretical methods [3,20,21]. Among spectroscopic investigations of water structure, the work of Tukhvatullin et al. [22] should be mentioned, where the polarized com- ponents of Raman spectra of O \\ H vibrations in liquid water were in- vestigated. It was shown that the experimentally observed broad band in the region 3000–3800 cm -1 in Raman spectra of liquid water can be viewed as a superposition of two systems of bands with different magnitudes of the depolarization ratio. One system of bands was pro- posed to be associated with the symmetric (low-frequency) O \\ H vi- bration of the water molecule. The other system of vibrational bands was proposed to be associated with the “antisymmetric” (high- frequency) vibration. This assignment was supported by quantum- chemical calculations on cluster models of local water structures [22], which show a red shift of the symmetric and antisymmetric vibrations with increasing number of molecules in the clusters. Moreover, the dis- tance between them increases from 100 cm -1 for the monomer to 200 cm -1 for the pentamer. Thus, having compared the experimental spectra of liquid water with results of calculations for various size clus- ter models the authors of [22] suggested the presence of aggregations consisting of at least five molecules in liquid water. Indeed, pentamers as the dominating smallest closed H-bond loop has been suggested for supercooled water by Russo et al. [23], but not as clusters but rather as topological features of the H-bonding network. This has recently been supported by Martelli et al. [24] based on analysis of ab initio molecular dynamics trajectories. An alternative interpretation of the two dominating bands in the liq- uid Raman spectrum and their dependence on temperature and salt concentration [25,26] is in terms of two predominant local H-bonding structures, respectively high- (HDL) and low-density liquid-like (LDL) reminiscent of the well-established HDA and LDA forms of the amor- phous ices [3]. This interpretation is directly related to scenarios to ex- plain the origin of the apparent divergence of response functions [27, 28] and is furthermore supported by interpretations of x-ray spectro- scopic data [3,29–31] although this is not without controversy [32–35]. To distinguish between spectral bands, which belong to clusters of a certain size, methods of their isolation in low-temperature matrices are often used [11–17,36–39]. As was shown in [40–42], the heating of hy- drogen-bonded liquids trapped in low-temperature matrices allows tracing the transformation of their cluster structure from monomers Journal of Molecular Liquids xxx (2016) xxx–xxx ⁎ Corresponding author. E-mail address: pvye@ukr.net (V. Pogorelov). MOLLIQ-06720; No of Pages 4 http://dx.doi.org/10.1016/j.molliq.2016.12.037 0167-7322/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Molecular Liquids journal homepage: www.elsevier.com/locate/molliq Please cite this article as: V. Pogorelov, et al., From clusters to condensed phase – FT IR studies of water, J. Mol. Liq. (2016), http://dx.doi.org/ 10.1016/j.molliq.2016.12.037