Infrared measurements of organic radical anions in solution using mid-infrared optical fibers and spectral analyses based on density functional theory calculations

By using ATR and transmission probes combined with bundles of mid-infrared optical fibers, high-quality infrared spectra are observed for the radical anions of biphenyl and naphthalene in deuterated tetrahydrofuran solutions. The ATR and transmission probes can be inserted into a glass-tube cell with O-rings under vacuum. Organic radical anions prepared separately in a vacuum system are transferred into the cell for infrared absorption measurements. Observed infrared spectra are in good agreement with those calculated by density functional theory. The origin of the strong infrared absorption intensities characteristic of the radical anions are discussed in terms of changes in electronic structures induced by specific normal vibrations (electron-molecular vibration interaction).