Home – Home – Jornals – Atmospheric and Oceanic Optics 2026 number 7

The absorption bands of bulk water are characterized by a mode structure determined by the presence of a network of hydrogen bonds between water molecules with different degrees of OH bonding. Determining the parameters characterizing water structure is important for studying external effects on water. The temperature dependence of the absorption band of bulk water corresponding to ν + δ combination band (4500-5600 cm^-1) was studied by Fourier-transform infrared spectroscopy in the temperature range from +10 to +90 °C. A technique for determining the sample temperature from its absorption spectrum in the 2 mm region was developed based on a regression analysis of the spectral data. The technique enables temperature estimation with an error of no more than 1-2 °C. Decomposition of the spectral contour revealed that the observed changes are due to a redistribution of intensity between constituent sub-bands (modes). These modes are interpreted as contributions from water molecules engaged in hydrogen bonds of different strengths. To characterize the structural state of water, a quantitative spectroscopic parameter C(T) is suggested, which is defined as the ratio of the intensity of the low-frequency mode (~ 4900 cm^-1), which characterizes the number of strongly bound water molecules, to the intensity of the high-frequency mode (~ 5200 cm^-1), which describes the number of weakly bound molecules. The value of C(T) systematically decreases with an increase in the water temperature, reflecting a reduction in the proportion of molecules with strong hydrogen bonds. The coefficient C(T) can be determined from a water absorption spectrum with a precision of ±4%. This approach provides a tool for investigating the effect of weak external perturbations on water structure.