Ab initio theoretical study of the electronic absorption spectra of polycyclic aromatic hydrocarbon radical cations of naphthalene, anthracene and phenanthrene

Ab initio calculations for the excited states of the positive ions of naphthalene, anthracene and phenanthrene have been carried out to elucidate their absorption spectra in the UV-VIS range (200–1000 nm). With restricted open-shell Hartree-Fock one-particle basis functions employing double-ζ or triple-ζ plus polarization AO basis sets and a multi-reference singles and doubles Cl, excitation energies of the π → π∗ states with relative errors generally below 1000 cm−1 are obtained. The frozen σ-core approximation employed provides a good description of the excitation energies and oscillator strengths which are of particular importance for astrophysical implications.