Photoacoustic measurements as a function of temperature in the range (294.1-308.2) K were used to determine the enthalpy and volume changes for the photoinduced dissociation at 266 nm of peroxodiphosphate ions in water. The analysis of the data, which considered the temperature dependence of the photodissociation quantum yield and of the thermoelastic parameters of the medium, yielded enthalpy and volume changes of (77 +/- 18) kJ mol(-1) and (12 +/- 1) ml mol(-1), respectively. These values are compared with those reported for other systems. (C) 2003 Elsevier Science B.V. All rights reserved.