VALENCE BOND MODEL FOR $^{1}n\pi^{*}$ STATES OF 2,2$'$,4,4$'$-TETRAMETHYLCYCLOBUTANE-1,3-DIONE (TMCBD)

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1983

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Ohio State University

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The ultraviolet absorption spectrum of TMCBD has been interpreted in terms of four [R. Spafford, J. Baiardo, J. Wrobel and M. Vala, J. Am. Chem. Soc. 98, 5217(1976)] and three [R. D. Gordon, M. Caris and D. G. Newman, J. Mol. Spectrosc. 60, 130(1976)] low-lying $^{1}n\pi^{*}$ states. We report valence bond calculations, which emphasize the localized nature of the $n\rightarrow\pi^{*}$ excitations on the carbonyl oxygens. The results show that there are only tow low-lying $^{1}n\pi^{*}$ states $\langle 1^{1}A_{u}$ and $1^{1}B_{1g}\rangle$ with the next set $\langle 2^{1}A_{u}$ and $2^{1}B_{1g}\rangle$ lying at last 3 eV higher. The spectra are reinterpreted in light of the valence bond calculations. Comparison with calculations on CBD reveals the important through-bond interactions induced by the methyl groups in TMCBD. Ionization from the oxygen lone pairs will also be considered.

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Author Institution: University of California, Los Alamos National Laboratory; Thompson Chemical Laboratory, Williams College

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