# THE GEOMETRICAL STRUCTURE OF BENZENE IN THE $^{1}B_{2**}$ EXCITED ELECTRONIC STATE

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 Title: THE GEOMETRICAL STRUCTURE OF BENZENE IN THE $^{1}B_{2**}$ EXCITED ELECTRONIC STATE Creators: McKenzie, R. D.; Watkins, I. W.; Coon, J. B. Issue Date: 1962 Publisher: Ohio State University Abstract: It is known that the $2600 {\AA}$ band system of benzene arises from a $^{1}B_{2**} \longleftarrow ^{1}A_{1g}$ electronic transition, which is forbidden for the equilibrium nuclear configuration but is made allowed by an $e_{2g}$ vibration. An approximate method of determining the geometrical structure of a polyatomic molecule in an excited electronic state has been $reported^{1}$. In the present work this method, which is based on the Franck-Condon principle, is used to determine the geometrical structure of the $^{1}B_{2u}$ state. Of the four excited state structures consistent with the observed $intensities^{2}$, the structure $(r_{CC} = 1.397 {\AA} + 0.037 {\AA}, r_{CH} = 1.084 {\AA} - 0.008 {\AA})$ was chosen. This choice was based on the fact the the C-H stretching frequency $\nu_{1}$ increases in the transition, while the C C stretching frequency $\nu_{2}$ decreases. The increase of $r_{CC}$ agrees with the value given by $Craig^{3}$. The corresponding change in the rotational constant $\Delta B = -0.0086 cm^{-1}$ compares well with $\Delta B = -0.0083 cm^{-1}$ obtained from the rotational structure. Description: $^{1}$ J. B. Coon, R. E. DeWames, and C. M. Loyd, J. Mol. Spec. (In Press). $^{2}$ L. Lang, Absorption Spectra in the Ultraviolet and Visible Region, p. 367 Academic Press, Inc., New York, 1961. $^{3}$ D. P. Craig, J. Chem. Soc. p. 2146 (1950). Author Institution: Physics Department, Agricultural and Mechanical College of Texas, URI: http://hdl.handle.net/1811/14369 Other Identifiers: 1962-B-2