Pressure Tuning Spectroscopic Study of Electron-Tunnelling Processes in Solution

The first study of the effect of pressure on the intervalence transfer (IT) band of a very weakly coupled mixed valence binuclear, (μ-2,6-dithiaspiro[3.3]heptane)decaamminediruthenium(II,III) hexafluorophosphate in D₂O is reported. A red shift of more than 200 cm^-1 and a small increase in the oscillator strength of the IT band were observed over a pressure range of 1500 bars. These effects were interpreted as arising primarily from H-bonding between the ammine groups on the ruthenium atoms and the solvent D₂O molecules. A nonadiabatic, multiphonon electron-tunnelling theory was employed to calculate rates of thermal electron transfer at each pressure, and ΔV^‡ was estimated to be -7.5 ± 0.2 cm³/mol for the thermal electron exchange.