A NEW METHOD FOR THE DETERMINATION OF THE BARRIER TO INTERNAL ROTATION IN A SYMMETRIC TOP MOLECULE
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Date
1978
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Ohio State University
Abstract
A technique has been developed for the first time to determine to high accuracy the barrier to internal rotation in a symmetric rotor. Only spectra in the ground vibronic state are required. The determination is made with a molecular beam electric resonance spectrometer by extending the avoided crossing method developed $^{e}arlier {1,2}$ Normally forbidden transitions obeying the selection rules $\Delta K=\pm 1, \pm 2, \pm 3$ and $\Delta \sigma =0, \pm 1$ have been observed in $CH_{3}CF_{3}$. Here $\sigma$ is the quantum number distinguishing the different torsional sublevels of the ground torsional state. The $(\Delta \sigma = \pm 1)$ transitions do not conserve torsional symmetry; no transitions of this type have been previously reported. It has been found that the reduced barrier height s = 89.20 (7), the moment of inertia of the $CH_{3}$-top $I\alpha=5.28(18)\times 10^{-40}\; gm-cm^{2}$ and the barrier to internal rotation $V_{3} = 3.15(11)$ Kcal/mole. In addition, the dipole moment $\mu_{D}$ bas been shown to be independent of $\sigma$ at the 1\% level. Values will be given for $\mu_{D}$ and the rotational constant $A_{O}$ about the symmetry axis.
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$^{1}$W. L. Meerts and I.. Ozier, Fifth Colloquium on High Resolution Molecular Spectroscopy, Tours, France (September, 1977). $^{2}$I. Ozier and W. L, Meerts, Phys. Rev. Lett. \emph{40}, 226 (1978). I. Ozier had been on sabbatical leave (1976-77) from the Department of Physics, University of British Columbia, Vancouver, Canada.""
Author Institution: Fysisuh Laboratorium, Katholieke Universiteit
Author Institution: Fysisuh Laboratorium, Katholieke Universiteit