2 CALORIMETRICALLY DISTINCT STATES OF LIQUID WATER BELOW 150 KELVIN

Vapor-deposited amorphous solid and hyperquenched glassy water were fo und to irreversibly transform, on compression at 77 kelvin, to a high- density amorphous solid. On heating at atmospheric pressure, this soli d became viscous water (water B), with a reversible glass-liquid trans ition onset at 129 +/- 2 kelvin. A different form of viscous water (wa ter A) was formed by heating the uncompressed vapor-deposited amorphou s solid and hyperquenched liquid water. On thermal cycling up to 148 k elvin, water B remained kinetically and thermodynamically distinct fro m water A. The occurrence of these two states, which do not interconve rt, helps explain both the configurational relaxation of water and str ess-induced amorphization.