ABSTRACT The unique properties of water can be explained by its cluster structure. Earlier FTIR studies of water trapped in low-temperature inert matrices demonstrated a temperature evolution of water vibrational spectra, which can be considered as a manifestation of structure transformations in the sample. Raman spectra of water in a wide temperature range contain a broadband background between 1000 and 2500 cm-1. The intensity of the background band decreases with heating of the liquid. It is consistent with an increase in the high-frequency wing of the OH stretching band, caused by a decrease in the number of pentamers and an increase in the number of smaller clusters in liquid water with increasing temperature. The broadband background is associated with the formation of super-molecular structures in the liquid water, in which standing waves of electron density can arise. The calculated linear size of the corresponding super-molecular structure is 10 Ǻ, that correlates with estimated size of water pentamers. In Raman spectra of water in solid state (at temperatures below 0 ºC), where the number of pentamers is essentially lower, the broadband background is not observed.
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