Excited states and intermediates by time-resolved infrared spectroscopy

For coordination compounds containing CO or CN groups, fast Lime-resolved i nfrared spectroscopy (TRIR) provides a convenient method of probing excited states and intermediates. TRIR has proved particularly powerful for probin g the structure and kinetics of organometallic intermediates. The interpret ation is particularly straightforward when combined with IR data from matri x isolation experiments, although there can be some subtle differences. In excited state studies, shifts in nu(CO) and nu(CN) frequencies, from ground to excited state, are sensitive to the changes in electron distribution on excitation, thus allowing the distinction between charge-transfer and non- charge-transfer transitions. Subtle effects on excited state nu(CO) band po sitions occur with change from fluid to rigid solvent-"infrared rigidochrom ism". There is often a change in nu(CO) bind width on excitation; this can be interpreted in terms of specific interactions between the excited specie s and the solvent. This paper presents some of our recent work in this area .