Electronic Spectra of Radical Cations and Their Correlation with Photoelectron Spectra

Abstract

Electronic absorption spectra of the radical cations of 1.2,7.8-dibenzochrysene, 1.2,3.4-dibenzanthracene, 1.2,5.6-dibenzanthracene and 1.2,7.8-dibenzanthracene in boric acid are measured. The transition energies of the cations are calculated using the Longuet-Higgins-Pople and Wasilewski type Open-Shell-SCF-MO methods with limited CI. A comprehensive discussion of the absorption bands is given in the light of the calculations and the photoelectron spectral data for the hydrocarbons. The correspondence between the optical and photoelectron spectra is found to be extremely good with almost negligible matrix shifts, thus highlighting the role of photoelectron spectroscopy in understanding the optical spectra of the radical cations and vice versa. Finally, a correlation diagram for the observed electronic transitions for the radical cations of anthracene and its benzologs is presented from which it is inferred that the optical A-transitions have some sort of correlation with the first IP's of the respective hydrocarbons.