  X-ray Raman spectra of liquid, sub- and super- critical water at the oxygen
K-edge were measured, at densities 1.02 - 0.16 gcm^-3. Measurements were made
along both an isotherm and an isochore passing near the critical point. As
density is reduced there is a general tendency of the spectra to increasingly
resemble that of the vapor phase, with, first, a well separated low-energy
peak, and, eventually, at densities below the critical density, peaks appearing
at higher energies corresponding to molecular transitions. The critical point
itself is distinguished by a local maximum in the contrast between some of the
spectroscopic features. The results are compared to computed X-ray absorption
spectra of supercritical water.
