Influence of impurities on two-level systems in amorphous ice

High-density amorphous (HDA) ice has a two-level system (TLS) optical density of states with a strength comparable to that found in many conventional glasses, whereas for the low-density amorphous (LDA) phase the TLS strength is at least 30 times smaller. Isotopic substitution resulting in 50% of the molecules having lower symmetry fails to change this strength ratio suggesting that the observed difference is not due to a breaking of the tetrahedral selection rule in the HDA phase. By doping the samples with different concentrations of LiCl, methanol, HF, NaCl, LiOH, and NaOH we have explored both the defect-induced TLS optical density of states and the glass transition characteristics in the LDA ice phase. (C) 2002 Elsevier Science B.V. All rights reserved.