A DOUBLE-MINIMUM POTENTIAL IN THE EXCITED STATE OF THE $2491 {\AA}$ BAND SYSTEM OF $NO_{2}$.
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Date
1967
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Ohio State University
Abstract
The very large isotope shift $\sigma(N^{16}O_{2})-\sigma(N^{18}O_{2}) = - 19 cm^{-1}$ of the $(000)\leftarrow(000)$ band at $\Sigma 491 {\AA}$ can be explained only in terms of a very small frequency in the antisymmetrical mode of the excited electronic state. Photographs of the absorption spectra yield the isotope shifts $\Delta \nu^{\prime}_{1}, \Delta\nu^{\prime}_{2}, \Delta \nu^{\prime \prime}_{1}$ and $\Delta \nu^{\prime \prime}_{2}$. The frequency of the antisymmetrical mode of the ground state is $\nu^{\prime \prime}_{3} = 1618 cm^{-1}$ and the isotope shift of the zero-point energy in this mode is $\Delta G_{3}^{\ast}(0) = 15.5 cm^{-1}$. Hence sufficient information is available for calculating the zero-point energy in the antisymmetrical mode of the excited state. The preliminary result is $\Delta G_{3}^{1}(0) = 3.5 cm^{-1}$. A strong semidiffuse band $714 cm^{-1}$ toward the violet side of the $(000)\leftarrow(000)$ band cannot be explained in terms of symmetrical $frequencies.^{1}$ We have assigned this interval to $2 \nu_{3}^{1}\equiv 1^{+}-0^{+}$ of a double-minimum potential. The double-minimum potential allows a quantitative explanation of the band interval, its isotope shift and the relative intensity of the band. The tentative value for the barrier is $600 cm^{-1}$. This work was supported by the U.S. Air Force Office of Scientific Research. $^{1}$ R. K. Ritchie, A. D. Walsh and P. A. Warsop, Conference on Spectroscopy, Edited by M. J. Wells, Pergamon Press Ltd., London, 1962, p. 289.
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Author Institution: Department of Physics, Texas A. and M. University