A new approach to the spectral study of unstable radicals and ions in solution by the use of an inert gas glovebox system: observation and analysis of the infrared spectra of the radical anion and dianion of p-terphenyl

By using a Fourier-transform infrared spectrometer contained in an inert gas glovebox system (oxygen and water concentrations: <0.1 ppm), high-quality infrared absorption spectra have been observed for the radical anion and dianion of p-terphenyl in tetrahydrofuran solutions. Density functional theory with the B3LYP nonlocal exchange-correlation functional and the 6-311+G** basis set has been used for the calculations of the structures and infrared spectra of the neutral species, radical anion, and dianion of p-terphenyl. The observed infrared spectra of the radical anion and dianion are in good agreement with those calculated by density functional theory. The origin of the strong infrared absorption intensities characteristic of the radical anion and dianion are discussed in terms of changes in electronic structures induced by specific normal vibrations (electron-molecular vibration interaction).