Effects of Deposition Temperature on Phase Transition of Amorphous Ice

To investigate the effects of deposition temperature, Td, on the phase transition of amorphous ice with heating, the infrared spectra of ice deposited at temperatures of 6–160 K were measured. From the changing rate of the wavenumber of the O–H symmetric stretching mode with heating, the transition processes from high-density amorphous (HDA) ice to crystalline hexagonal ice Ih via low-density amorphous (LDA) ice and ice Ic were analyzed. The results show that the structure of the deposited ice depends on Td and is classified into six types: (i) HDA ice at Td < 20 K, (ii) a mixture of HDA and LDA ice at 20 K < Td < 80 K, (iii) LDA ice at 80 K < Td < 130 K, (iv) a mixture of LDA ice and Ic at 130 K < Td < 140 K, (v) Ic at 140 K < Td < 150 K, and (vi) a mixture of Ic and Ih at Td > ∼150 K. Furthermore, the processes of the structural transitions from the deposited ice with heating reflect Td. These results have important implications for the chemical evolution processes in interstellar molecular clouds.