Vibrational and electronic spectra of matrix-isolated pentacene cations and anions

Pentacene cations and anions have been formed by electron bombardment of a vapor phase mixture of pentacene, Ar and CCl4 and trapped in an argon matrix. The electronic and infrared spectra of both ions have been recorded. Increasing concentrations of CCl4 resulted in the eventual disappearance of the anion spectrum. The intensity distributions of the IR spectra of the ions are similar but differ markedly from the distribution of neutral pentacene. The ion intensities resemble the distribution of the so-called interstellar ‘unidentified infrared’ bands. The visible bands of neutral, cationic and anionic pentacene are compared with the diffuse interstellar bands.