Harmonic oscillations of the concentration of H-bonds in liquid water

A new effect lying in a periodic structural overheating-overcooling in water is demonstrated. The effect is manifested as oscillations of the center of the OH Raman band excited with the second-harmonic radiation of a Nd:YAG laser. The oscillation period is 22–48 s, whereas the oscillations are observed over an interval of longer than 16 min. The equilibrium center of the Raman band is monotonically shifted towards water over-cooling upon pulsed laser irradiation. The physical nature of the effect is discussed using a two-liquid model of water as a nonequilibrium system.