Fig. 1.

Two possible scenarios to explain the metastable phase behavior of deeply supercooled water based on experimental literature T_g data for LDA (filled black triangle) (4–6) and HDA (filled black circles) (14) and compared with glass transition temperatures from computer simulations (lines) (17). The single T_g scenario, in A indicated by the dash-dotted line, is qualitatively similar to the situation found in water simulations using the SPC/E model (17), whereas the double T_g scenario in B is qualitatively similar to the situation found for the ST2 model (17). The dashed line corresponds to the T_g,2 line for HDA, whereas the dotted line corresponds to the predicted T_g,1 line for LDA. The observation of a second T_g (open circle) at ambient pressure reported in this work rules out the possibility of a single T_g scenario.