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Title:1- And 2-dimensional Potental Functions When V3 Is Not The Barrier
Author(s):Groner, Peter
Subject(s):Mini-symposium: Large Amplitude Motions
Abstract:In simple cases of methyl group internal rotation, the barrier to internal rotation is equal to the $V_{3}$ coefficient in the standard equation of the potential function. In the past few years, methyl internal rotation potentials have been reported with significant $V_{6}$ contributions, of which p-toluic acid is just one example.\footnote{E.G. Schnitzler, et al., J. Phys. Chem. A 121 (2017) 8625} For $|V_6| << |V_{3}|$, the barrier is still $|V_3|$. However, if $0 < |V_{3}/V_{6}| < 4$, there are now two different barriers because there are two different potential minima (or maxima), and none of the barriers is equal to $|V_{3}|$ or $|V_{6}|$. Their difference is exactly $|V_3|$ but, for $V_3 > 0 $ and $V_6 < 0 $, the lower barrier is equal to $-V_{6}(1+V_{3}/(4 V_{6}))^2$. It is therefore incorrect to say that $|V_3|$ or $|V_{6}|$ is the barrier. Of course, corresponding effects are also present in systems with two or more internal rotors. However, in 2-D systems, additional minima and/or maxima may occur when potential interaction terms become significant, e.g. when $V_{33}$ and/or $V'_{33}$ have magnitudes similar to $V_{3}$ in a molecule like acetone (molecular symmetry group $G_{36} = [33]C_{2v}$). A number of examples for 1-D and 2-D systems are given and some consequences for the spectroscopy are discussed.
Issue Date:2021-06-22
Publisher:International Symposium on Molecular Spectroscopy
Genre:Conference Paper / Presentation
Date Available in IDEALS:2021-09-24

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