Thermodynamic changes associated with the formation of the hydrated electron after photoionization of inorganic anions: a time-resolved photoacoustic study.

The enthalpy and volume changes, deltaH and deltaV, associated with the 266 nm laser-induced photoionization reactions of aqueous ferrocyanide and iodide ions, to yield the hydrated electron, e(-)aq, and oxidized products were determined by temperature-dependent time-resolved photoacoustics. The photoionization quantum yield as function of temperature (9-30 degrees C) was determined by laser flash photolysis actinometry. The obtained values were used for the calculation of thermodynamic parameters associated with the formation of e(-)aq, such as the apparent partial molar volume, V(o)e = 26 cm3 mol(-1), and the standard formation enthalpy and entropy changes, deltaH(o)f,e = 31 kJ mol(-1) and TdeltaS(o)f,e = 338 kJ mol(-1). These results indicate that the formation of the aqueous excess electron solution is governed by the increase in entropy in the three-dimensional hydrogen-bonding network of water.