Laser-induced optoacoustic spectroscopy has been applied to the photoinduced electron-transfer reaction between Ru(bpy)(3)(2+) and various salts of Fe(III) [Fe(ClO4)(3), Fe-2(SO4)(3), and FeCl3]. The reaction volume changes associated with photoinduced ligand exchange derived from these measurements allowed the determination of partial molar volumes at high dilutions of several species such as FeSO4, FeSO4+, Fe(SO4)(2)(-), Fe(OH)(2+), FeCl+, FeCl2+, and FeCl2+, not attainable from other techniques. The volume change of oxidation of Ru(bpy)(3)(2+) to Ru(bpy)(3)(3+) at high dilution was also calculated.