Formation of amorphous ice by careful annealing of ice XII

Thermally induced transformations of ice XII were characterized using the Raman spectra of the isolated O-D vibration of 5% HDO molecules in H2O ice XII. Spectra were collected continuously as samples were annealed between 77-160 K. Raman spectra first show a sharp peak centered on Delta nu =2424 cm(-1) from ice XII at 120 K. As the sample is further annealed isothermally at 120 K this peak broadens and shifts to higher frequency Delta nu =2439 cm(-1) and full width at half maximum 65 cm(-1). indicating the production of low-density amorphous ice by decompression amorphization. Ice Ic is formed upon further annealing at 130-140 K. The local hydrogen bond strength of the resulting amorphous phase was found to be close to that of glassy water.