Electronic Spectra of Radical Cations and their Correlation with Photoelectron Spectra. VI. A Reinvestigation of Two-, Three-, and Four-Ring Condensed Aromatics

Earlier interpretations of the electronic spectra of two-, three-, and four-ring condensed aromatic hydrocarbon radical cations are reexamined in the light of the UV photoelectron spectroscopic data for their neutral precursors and improved open-shell self-consistent field configuration interaction (SCF-CI) calculations. From the electronic transition energies for some 33 aromatic radical cations obtained from electronic absorption spectra (EAS) and those inferred from photoelectron spectra (PES), the following correlation is found between the two types of spectroscopies: E$\text{}_{EAS}$ = (0.23 ± 0.20) + (0.98 ± 0.01)E$\text{}_{PES}$. The slope of this line is very close to unity which shows that the matrix shift on going from the solid phase (electronic spectrum) to the vapour phase (PE spectrum) is almost negligible and that there is no appreciable change in the geometry of the molecules on ionization.