Electronic absorption spectroscopy of polycyclic aromatic hydrocarbons (PAHs) radical cations generated in oleum: A superacid medium

Oleum (fuming sulphuric acid), a well known superacid, was used as medium for the generation of the radical cation of a series of selected PAHs. The resulting radical cation spectra were studied by electronic absorption spectroscopy. Not only common PAHs like naphthalene, anthracene, tetracene, pentacene, perylene, pyrene, benzo[a]pyrene, phenanthrene and picene were studied but also the less common and very large PAHs relevant also for the astrochemical research, like coronene, hexabenzocoronene, quaterrylene, dicoronylene and a coronene oligomer. A correlation between the first ionization potential (I(P1)) of the PAHs studied and the energy to the so-called A-type band of the radical cations observed in oleum has led to the equation I(P1) = 1.30E(A) + 4.39 (in eV) which permits to estimate the energy of the PAHs radical cation transition (E(A)) in the VIS-NIR knowing the relative ionization potential or vice versa. (c) 2010 Elsevier B.V. All rights reserved.