Effects of Deposition Temperature on Phase Transition of Amorphous Ice

To investigate the effects of deposition temperature, T d, 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 I h via low-density amorphous (LDA) ice and ice I c were analyzed. The results show that the structure of the deposited ice depends on T d and is classified into six types: (i) HDA ice at T d < 20 K, (ii) a mixture of HDA and LDA ice at 20 K < T d < 80 K, (iii) LDA ice at 80 K < T d < 130 K, (iv) a mixture of LDA ice and I c at 130 K < T d < 140 K, (v) I c at 140 K < T d < 150 K, and (vi) a mixture of I c and I h at T d > ∼150 K. Furthermore, the processes of the structural transitions from the deposited ice with heating reflect T d. These results have important implications for the chemical evolution processes in interstellar molecular clouds.