CH3 Internal Rotation in 9-METHYLANTHRACENE
Abstract
We observed the rotationally resolved fluorescence excitation spectrum of the S1 ← S0 transition of jet-cooled 9-methylanthracene. The potential energy curve for CH3 internal rotation is six-fold symmetric. The barrier to rotation (V6) is ∼ 120 cm-1 [2], which is considerably larger than that of toluene ( ∼ 5 cm-1 ) [1]. The V6 value is the energy difference between two isomers 'staggered' and 'eclipsed'. The main contribution to V6 is expected to be hyperconjugation, which is the π-like interaction between the aromatic π orbital and methyl sp3 orbital.
The final goal of this work is to quantitatively elucidate the vibrational and rotational energy levels for CH3 internal rotation. It is essential to observe the high-resolution and high-precision electronic spectra and theoretically search the best effective Hamiltonian to reproduce the experimental results. We are now developing a new laser control system with optical frequency comb locked to GPS, and an ab initio method which provides the reliable potential energy curve. [1] M. Baba, et al., J. Phys. Chem. A {113}, 2369 (2009) [2] D. R. Borst and D. W. Pratt, J. Chem. Phys. {113}, 3658 (2000)- Publication:
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74th International Symposium on Molecular Spectroscopy
- Pub Date:
- June 2019
- DOI:
- 10.15278/isms.2019.MI08
- Bibcode:
- 2019isms.confEMI08B
- Keywords:
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- Large amplitude motions;
- internal rotation