Theoretical study of the vertical electron excitation of linear carbon clusters C-3, C-5, and C-7

The vertical electron excitation spectra of linear carbon clusters C-3, C-5 , and C-7 have been investigated by means of polarization propagator calcul ations using the second-order algebraic diagrammatic construction [ADC(2)] scheme. The structure of singlet and triplet excited-state manifolds below the lowest ionization threshold has been analyzed in detail for the smalles t prototype cluster C-3. The electronic spectra of all three molecules cont ain numerous low-lying single and double valence excitations, reflecting st rongly the correlated nature in these clusters. The density of the excited states becomes increasingly high above the onset of Rydberg excitations. A substantial mixing of various valence and Rydberg configurations in this re gion does not allow for simple interpretation of the final electronic state s. The spectroscopic and photophysical implications of this complex situati on are discussed. Where possible the computed excitation energies and oscil lator strength are compared with available experimental and previous theore tical data. (C) 2001 John Wiley & Sons, Inc.