The anomalous behavior of the density of water in the range 30 K < T < 373 K.

The temperature dependence of the density of water, rho(T), is obtained by means of optical scattering data, Raman and Fourier transform infrared, in a very wide temperature range, 30 < T < 373 K. This interval covers three regions: the thermodynamically stable liquid phase, the metastable supercooled phase, and the low-density amorphous solid phase, at very low T. From analyses of the profile of the OH stretching spectra, we determine the fractional weight of the two main spectral components characterized by two different local hydrogen bond structures. They are, as predicted by the liquid-liquid phase transition hypothesis of liquid water, the low- and the high-density liquid phases. We evaluate contributions to the density of these two phases and thus are able to calculate the absolute density of water as a function of T. We observe in rho(T) a complex thermal behavior characterized not only by the well known maximum in the stable liquid phase at T = 277 K, but also by a well defined minimum in the deeply supercooled region at 203 +/- 5 K, in agreement with suggestions from molecular dynamics simulations.