THE PUZZLING STATISTICAL PHYSICS OF LIQUID WATER

Although H2O has been the topic of considerable research since the beg inning of the century, the peculiar physical properties are still not well understood. We discuss recent experiments and simulations relatin g to the hypothesis that, in addition to the known critical point in w ater, there exists a ''second'' critical point at low temperatures. in particular, we discuss very recent measurements of the compression-in duced melting and decompression-induced melting lines of high-pressure forms of ice. We show how knowledge of these lines enables one to obt ain an approximation for the Gibbs potential G(P, T) and the equation of state V/(P, T) for water, both of which are consistent with the pos sible continuity of liquid water and the amorphous forms of solid wate r. We also comment on some of the evidence that is equally consistent with other scenarios for the behavior of liquid water. (C) 1998 Elsevi er Science B.V. All rights reserved.