title: UV/visible spectroscopy of matrix-isolated hexa-peri-hexabenzocoronene: Interacting electronic states and astrophysical context.
abstract: Absorption spectra of hexa-peri-hexabenzocoronene isolated in rare-gas matrices are reported for the wavelength range between 200 and 500 nm. Measurements were carried out in neon and in argon at 5.8 and 12.0 K, respectively. Calculations based on semiempirical models and on density-functional theory were performed to assign the observed features. The electronically excited states involved in Clar's alpha- and p-bands are identified as S(1)(B(2u)) and S(2)(B(1u)), respectively. Although the upper state associated with the beta-band is found to be a (1)E(1u) state, it remains undetermined whether it is S(3) or S(4). Structures in the beta-band are interpreted as resulting from the interaction between the (1)E(1u) state and the e(2g) vibrational manifold of S(2)(B(1u)). The new measurements are used to narrow down the wavelength ranges where the bands of hexa-peri-hexabenzocoronene should be found in the gas phase. A previous estimate of the interstellar abundance of this polycyclic aromatic hydrocarbon is discussed.
authors: Laboratory Astrophysics Group of the Max Planck Institute for Astronomy at the Friedrich Schiller University Jena, Institute of Solid State Physics, Helmholtzweg 3, D-07743 Jena, Germany.
authors: Gaël
authors: G
authors: Rouillé
authors: Mathias
authors: M
authors: Steglich
authors: Friedrich
authors: F
authors: Huisken
authors: Thomas
authors: T
authors: Henning
authors: Klaus
authors: K
authors: Müllen