Internal rotation of methyl group in 2- and 1-methylanthracene studied by electronic spectroscopy and DFT calculations

Masayuki Nakagaki, Eriko Nishi, Kenji Sakota, Kaori Nishi, Haruyuki Nakano, Hiroshi Sekiya

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Abstract

The S1-S0 fluorescence excitation and dispersed fluorescence spectra of 2- and 1-methylanthracene are measured in a supersonic free jet expansion. The barrier heights to internal rotation in the S 0 and S1 states of 2-methylanthracene are determined to be 69 and 335 cm-1, respectively, by using a one-dimensional free-rotor model. A prominent 0-0 transition has been observed in the fluorescence excitation spectrum of 1-methylanthracene, but no methyl rotational bands have been detected in both the excitation and dispersed fluorescence spectra. The potential energy curves of the methyl rotation are obtained for 2- and 1-methylanthracene with density functional theory (DFT) calculations and time-dependent (TD)-DFT calculations at the B3LYP/6-31 + G(d,p) level. The barrier heights and the phase of the potential energy curve are very different between 2- and 1-methylanthracene and substantially depend on the electronic state. These differences are consistently explained by a π*-σ * hyperconjugation effect introduced by Nakai and Kawai [Chem. Phys. Lett. 307 (1999) 272].

Original languageEnglish
Pages (from-to)178-184
Number of pages7
JournalChemical Physics
Volume316
Issue number1-3
DOIs
Publication statusPublished - Sep 19 2005

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All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Spectroscopy
  • Atomic and Molecular Physics, and Optics

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