We report studies of the coupling of vibrational excitations to photoinduced electron transfer in a mixed-valence transition metal complex [(CN)(5)OsCNRu(NH3)(5)](-) Static metal-metal charge transfer (MMCT) spectra, infrared (IR) absorption spectra at different temperatures, resonance Raman spectra, and polarized light transient spectra were taken to reveal the solvent and vibrational coupling to reverse electron transfer. The measured reverse electron transfer rates are greater than 3 x 10(12) s(-1). We observe excitations in the non-totally symmetric vibrational mode accompanying the reverse electron transfer process in both formamide (FA) and deuterium oxide (D2O) solutions. A simulation of the spectral dynamics in FA and D2O solutions is presented using a kinetic model for vibrational excitation and relaxation. The simulation includes the effect of solvent heating through coupling a low-frequency mode to a medium-frequency oscillator. The vibrational relaxation times of trans CN obtained from the spectral fits show faster vibration relaxation in D2O than FA, reflecting an overlap of the IR absorption spectra of the solvent and the CN vibrations.