JOURNAL OF RAMAN SPECTROSCOPY J. Raman Spectrosc. 2005; 36: 771–776 Published online 16 May 2005 in Wiley InterScience (www.interscience.wiley.com). DOI: 10.1002/jrs.1359 Comparison of Raman spectroscopic methods for the determination of supercooled and liquid water temperature Dubravko Risovi ´ c ∗ and Kre ˇ simir Furi ´ c Molecular Physics Laboratory, Rudjer Bo ˇ skovi ´ c Institute, POB 180, HR-10002 Zagreb, Croatia Received 5 January 2005; Accepted 24 February 2005 Raman spectroscopy provides an efficient method for non-contact determination of liquid water temperature with high spatial resolution. It can be also used for remote in situ determination of subsurface water temperature. The method is based on temperature-dependent changes of the molecular O–H stretching band in the Raman spectra of liquid water. These in turn are attributed to a decrease in intermolecular hydrogen-bonding interactions with increase in temperature. Here, the results of an experimental study employing three different approaches in the determination of temperature from recorded O–H stretching band in the Raman spectra of liquid and supercooled water are presented and discussed. The first two methods are based on deconvolution of the spectral band into Gaussian components whose intensities and associated specific spectral markers are temperature dependent, and the third approach is based on Raman difference spectroscopy (RDS). The presented measurements were conducted on distilled and deionized supercooled and liquid water in the temperature range between −12.5 and +32.5 ◦ C. The results are compared in terms of linearity of response, sensitivity and accuracy. It is shown that the method based on RDS even in the supercooled temperature range provides better accuracy (the standard deviation from the true temperature is ±0.4 K) and linearity in temperature determination than more complicated methods based on Gaussian deconvolution of the O– H stretching band. Copyright  2005 John Wiley & Sons, Ltd. KEYWORDS: temperature determination; water; supercooled water; Raman difference spectroscopy; H-bonding INTRODUCTION Water should be a simple example of molecular structure, with three vibrational normal modes: a bending and sym- metric and antisymmetric stretching. However, the structure of the molecule with two donor and one acceptor cen- ter results in a temperature-dependent H-bonded network. Consequently, owing to the ability (existence) of intermolec- ular hydrogen bonding and electrostatic interactions, liquid water has a very complex structure that is still not com- pletely elucidated. 1–3 This structure is rather soft because of the anharmonicity of the hydrogen bond and its rela- tively low energy. Hence the structure is sensitive to changes in temperature and to the presence of ions in solution. 4–6 Although it is generally assumed that ions dissolved in L Correspondence to: Dubravko Risovi´ c, Molecular Physics Laboratory, Rudjer Boˇ skovi´ c Institute, POB 180, HR-10002 Zagreb, Croatia. E-mail: drisovic@irb.hr Contract/grant sponsor: Croatian Ministry of Science, Education and Sports; Contract/grant numbers: 0098029; 0098022. liquid water have a strong effect on the hydrogen-bond structure of the liquid, a recent investigation questions this influence and indicates that the presence of ions has a neg- ligible effect on the hydrogen bonding in liquid water. 2 Hence a dominant influence on the structure should be associated with temperature effects. With increase in tem- perature, some of the H-bonds are disrupted, resulting in corresponding changes in the OH stretching vibrations rep- resented as a broad band in the Raman spectra in the range 2700–4000 cm 1 . Similar temperature-dependent behavior was also observed in an investigation of the OH stretching overtone (5500 – 8000 cm 1 ). 7 The Raman spectrum of liquid water in the range 2700–4000 cm 1 that originates from symmetric and anti- symmetric OH stretching vibrations is a broad band com- posed of several vibrational components that are influenced by intra- and intermolecular couplings. 8 Traditionally, it was modeled by a set of a few Gaussian components, and only recently a six-component Gaussian basis was derived based on Raman difference spectroscopy Copyright  2005 John Wiley & Sons, Ltd.