Raman Spectroscopy of the OH Group Vibrations in Structural Complexes of Liquid Water

Abstract

A number of spectral features in the structure of the OH band of water located at ∼3450 cm−1 are registered in a series of 34 Raman spectra. Each spectrum of the series is excited by a pair of successive secondharmonic pulses of a moderate intensity (15–20 MW/cm2) from a Nd:YAG laser operating at a pulse repetition frequency of 1 Hz. The pairs of pulses in the series follow at an interval of 15–20 s. It is found that, in ten measurements of the first series, there occur three successively reproduced spectra with an anomalously narrow band (down to 260 cm−1) and spectra with a local minimum in the range of 3400 cm−1. The occurrence of the latter spectra was predicted previously as a manifestation of the occurrence of structural fragments of water. In the range 3690–3700 cm−1, a narrow peak of free OH vibrations is observed, whose intensity decreases in subsequent series. Some Raman spectra are similar to the spectra of the OH vibrations of water clusters in molecular beams and surface layers. These data make it possible to assume that structural complexes exist in the volume of water irradiated by the laser beam, with the lifetime of some of them being no shorter than 40 s.