EFFECT OF PRESSURE ON PROTON-TRANSFER RATE IN AQUEOUS-SOLUTIONS - A PICOSECOND STUDY
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abstract
Time resolved picosecond fluorescence studies of excited aqueous 8-hydroxy-1,3,6-pyrene trisulfonate (HPTS) have been carried out at pressures up to the ice transition point of H2O and D2O. The proton transfer rates derived from these studies exhibit a large linear increase with pressure from 8 109 s-1 at 1 atm and 294 K to 2.5 1010 s-1 at the liquidice VI transition point at 9 kbar and 294 K. In D2O, the deuteron transfer rate also increases linearly with pressure from 2.7 109 s-1 at 1 atm to 1010 s-1 at 8 kbar. The rates between H 2O and D2O were found to differ by a factor of 3, which is consistent with the isotope effect kD+/kH+ = 1/3 which is maintained across the pressure range studied. From these results, an activation volume V0 of -6 cc/mol is obtained. These results which show different trends than previous NMR and proton conductance studies are discussed in terms of a microscopic model. 1984 American Institute of Physics.
