Reaction volume and enthalpy changes in photochemical reaction detected by the transient grating method; photodissociation of diphenylcyclopropenone

A method for the measurement of reaction volume (ΔV) and enthalpy (ΔH) changes of a photochemical reaction is presented based on the transient grating technique. Since ΔV and ΔH contributions are detected separately by the time-resolved manner, this new method does not require changing the temperature or the solvent. If the diffusion constants of the species are very different, the partial molar volume of each chemical species can be determined. This method is applied to the photodissociation reaction of diphenylcyclopropenone. This method also provides a very accurate and convenient way to measure the diffusion constant of gaseous molecules in liquids.