We report transient resonance Raman experiments that identify isodiiodomethane as the photoproduct responsible for the 385 nm absorption band observed following ultraviolet excitation of diiodomethane in liquid solutions. Comparison with previously reported gas-phase experiments and solution-phase resonance Raman and femtosecond transient absorption results suggest that solvation leads to appreciable production of the isodiiodomethane (H2C-I-I) photoproduct via the interaction of the initially formed CH2I and I fragments with the solvent cage. The isodiiodomethane photoproduct is likely the species or an intermediate to the species that reacts with alkenes in cyclopropanation reactions that use ultraviolet excitation of diiodomethane in liquids.