Time-Resolved, Step-Scan FTIR Spectroscopy of Excited States of Transition Metal Complexes

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Abstract
Time-resolved, step-scan Fourier transform infrared spectroscopy has been developed as a method of studying electronically excited states of transition metal complexes. The technique takes advantage of the unique properties of carbonyl and cyanide stretching vibrations, including high infrared oscillator strength and well established sensitivity of vibrational frequency, intensity, and bandwidth to electronic and molecular structure. Electronic excitation generally produces significant transient infrared absorption changes which are characteristic of the changes in electronic structure, such as oxidation of the metal. TRIR spectroscopy thus provides new insight on the nature of the excited state transition (e.g. charge transfer vs. ligand centered), the extent of charge transfer, communication between metal centers, and energy and electron transfer processes. The step-scan FTIR approach has significant advantages over conventional time-resolved techniques, including spectral multiplexing, increased IR throughput, and fast data acquisition, making it possible to rapidly obtain complete spectra with good sensitivity and time-resolution.