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

Abstract

The enthalpy and volume changes, ΔH and ΔV, 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 °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°_e⁻ = 26 cm³ mol⁻¹, and the standard formation enthalpy and entropy changes, ΔH°_f,e⁻ = 31 kJ mol⁻¹ and TΔS°_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.