CH3 internal rotation is one of the typical large amplitude motions in polyatomic molecules, the spectral analysis and theoretical calculations of which, were developed by Li-Hong Xu and Jon Hougen. We observed a Doppler-free high-resolution and high-precision spectrum of 9-methylanthracene (9MA) by using the collimated supersonic jet and optical frequency comb techniques. The potential energy curve of CH3 internal rotation is expressed by a six-fold symmetric sinusoidal function. It was previously shown that the barrier height (V6) of 9MA-d12 was considerably smaller than that of 9MA-h12 [M. Baba, et al., J. Phys. Chem. A 113, 2366 (2009)]. We performed ab initio theoretical calculations of the multicomponent molecular orbital method. The barrier reduction by deuterium substitution was partly attributed to the difference between the wave functions of H and D atomic nuclei.
Large amplitude motion in 9-methylanthracene: High-resolution spectroscopy and Ab Initio theoretical calculation†
Masaaki Baba, Ayumi Kanaoka, Akiko Nishiyama, Masatoshi Misono, Takayoshi Ishimoto, Taro Udagawa; Large amplitude motion in 9-methylanthracene: High-resolution spectroscopy and Ab Initio theoretical calculation. Chin. J. Chem. Phys. 1 February 2020; 33 (1): 8–12. https://doi.org/10.1063/1674-0068/cjcp1910188
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