Vibrational and electronic spectra of matrix-isolated tetracene cations

The electronic and vibrational spectra of tetracene cations, generated by vapor-phase electron bombardment and deposited in an argon matrix, have been recorded. Integrated intensities of the infrared bands of neutral and cationic tetracene compare well with a recent density functional calculation by Langhoff. As observed in previous studies of PAH ions, the intense neutral out-of-plane CH bends decrease drastically in the cation, while the very weak neutral in-plane CC stretches and CH bends gain dramatically upon ionization. The possible contribution of tetracene cations and neutrals to the ‘unidentified interstellar infrared’ bands is discussed.