ULTRAFAST ELECTRON-TRANSFER AND COUPLED VIBRATIONAL DYNAMICS IN CYANIDE BRIDGED MIXED-VALENCE TRANSITION-METAL DIMERS

Picosecond infrared spectroscopy has been used to investigate electron transfer and vibrational excitation and relaxation in the mixed-valence transition-metal dimer [(NC)5MIICNMIII(NH3)5]- (M = Ru, Os). Optical excitation into the metal-to-metal charge transfer band results in formation of the excited state redox isomer [(NC)5MIIICNMII(NH3)5]-. Subsequent back electron transfer results in reformation of the ground state and occurs with tau < 0.5 ps. Upon return to the ground electronic state, large amounts of energy (up to 7 quanta, 14 000 cm-1) are placed into the terminal MC=N stretching mode. The rate of the subsequent energy relaxation was measured; decay times ranged from <0.5 to 6 ps for the ruthenium analog and from 1.8 to 18 ps for the osmium analog. Results are compared to recent theoretical models of Jortner and Bixon.