<title>Picosecond infrared study of vibrational-dependent electron transfer rates</title>

Abstract

Photoinduced electron transfer and thermal back electron transfer in the inorganic donor- acceptor contact ion-pair {Cp<SUB>2</SUB>Co<SUP>+</SUP>Co(CO)<SUB>4</SUB><SUP>-</SUP>} have been observed in solution with picosecond time-resolved infrared absorption spectroscopy. Optical excitation of a charge transfer band created by cobalt interaction causes an immediate electron transfer to form a neutral pair, and the spontaneous return electron transfer is followed by monitoring the CO stretching frequencies of the Co(CO)<SUB>4</SUB><SUP>-</SUP> and Co(CO)<SUB>4</SUB> molecules. We have observed the back electron transfer decay for up to 3 quanta of the CO stretching mode in the neutral pair for dichloromethane solvent. The arrival kinetics into the ion pair and ion pair vibrational relaxation rates for final return to the vibrationless level have been studied for up to 4 quanta of vibration. These are the first measurements of an electron transfer process with vibrational resolution, and comparison to models is in progress.