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The absorption and fluorescence of anthracene in the near ultra-violet Katagiri, Seiko

Abstract

The fluorescence and absorption spectra of anthracene in the near ultra-violet were investigated in n-heptane, fluorene, biphenyl and n-hexane matrices at low temperature. The assignment of the excited electronic state as ‘Biu was confirmed. In the ground electronic state eight Qg and five b₃g, and in the 'Bᵢᵥ upper electronic state seven Qg and five b₃g fundamentals were assigned. It was deduced that the potential surfaces of the 'Ag and the 'Bᵢᵥ states were similar in shape as there was an approximate agreement between the values of corresponding fundamental vibrations in the two electronic states. The potential surfaces were unusually harmonic for a polyatomic molecule, at least along the normal co-ordinates available to this study. No evidence for the presence of anharmonicity was found in even the highest overtone (the third) measured, although several possible examples of Fermi resonance between vibrational modes were observed both in fluorescence and in absorption. The Fermi resonances were assigned primarily on the basis of intensity transfer between lines rather than line shifts. The presence of a weaker long-axis polarized transition ( 'B₂ᵥ- 'Ag ) in anthracene predicted by theory was not detected. The lowest energy electronic transition in fluorene was found to be polarized along the long axis of this molecule.

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