Temperature dependence of the mid-infrared OH spectral band in liquid water

We have studied the temperature dependence (14-57 degrees 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 degrees 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.