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 eluc idate their absorption spectra in the UV-VIS range (200-1000 nm). With restricted open-shell Hartree-Fock one-particle basis functions emplo ying double-zeta or triple-zeta plus polarization AO basis sets and a multi-reference singles and doubles CI, excitation energies of the pi --> pi states with relative errors generally below 1000 cm(-1) are ob tained. The frozen sigma-core approximation employed provides a good d escription of the excitation energies and oscillator strengths which a re of particular importance for astrophysical implications.