ChemInform Abstract: THE ELECTRONIC STATES OF THE PENTATETRAENE RADICAL CATION

HeIα excited photoelectron spectra of pentatetraene and the inferred ionization energies are reported. The first band has a characteristic Franck-Condon envelope similar to the first photoelectron bands of allene and butatriene. The four bands found below 16 eV ionization energy have been assigned to the X2E, A2E, B2E and C2B2 states of the radical cation of pentatetraene by comparison with STO-3G and SPINDO calculations on the cumulene series. The correlation scheme includes the 2s shell ionization energies of ethylene, allene and butatriene. The π-orbital ionization trends of the cumulenes are discussed in the framework of localized orbitals calculated with the STO-3G basis set.