Temperature dependence of proton diffusion in I_h ice

The temperature dependence of the proton diffusion constant, D _H+, in methanol-doped ice was studied over the wide temperature range of 80-260 K. For that purpose, we measured the time-resolved fluorescence of a flavin mononucleotide (FMN) and riboflavin in ice doped with HCl or HF. The analysis of the fluorescence quenching provided the value of D_H+. We found that the temperature dependence of D _H+ at T > 235 K is rather small, whereas at T <235 K, it is rather large. These temperature-dependence results are similar to previous conductivity measurements. We used a stepwise, two-coordinate qualitative proton transfer model to explain the temperature dependence of D_H+ in ice.