We report an ultrafast 400 nm pump-IR probe study of Mn-2 (CO)(10), photochemistry in cyclohexane and isopropanol at room temperature. While both Mn-2(CO)(9) and Mn(CO)(5) are produced with UV dissociation, long wavelength excitation at 400 nm yields predominantly the monometal product, Mn(CO)(5). The Mn(CO)(5) vibrational energy relaxation (VER) is analyzed in terms of the narrowing of its IR absorption band. The initial band broadening is attributed to population in low frequency vibrational modes (M-C stretches and bends) and the VER decay time is found to be on the 60 ps time scale in both solvents. (C) 2002 Elsevier Science B.V. All rights reserved.