Temperature Dependence of Proton Diffusion in Ih Ice

The temperature dependence of the proton diffusion constant, Drip, 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.