Temperature Dependence of the Mid-Infrared OH Spectral Band in Liquid Water

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Abstract
We have studied the temperature dependence (14–57 °C) of the OH-stretching vibration band in liquid water by the use of a microscope Fourier transform infrared (FT-IR) instrument with an attenuated total reflection (ATR) cell. In order to eliminate spectral distortions, we performed Kramers–Kronig transform of the ATR spectra and derived absorption- and refractive-index spectra. The numerical values are shown in detail. Application of principal component analysis (PCA) and partial least-squares 1 (PLS 1) modeling methods to the absorption-index spectra shows that the OH band consists of two abstract spectral components. The intensity of the first component changes linearly with temperature, whereas the second component changes nonlinearly, with a turning temperature around 30 °C. Each abstract spectrum has a pair of peaks, the intensities of which vary in an inverse manner with respect to each other for the temperature change.