Kinetics and Mechanism of the Photochemical Valence Tautomerization of Hexafluorobenzene

The kinetics of the photoisomerization of hexafluorobenzene to its ``Dewar'' isomer has been investigated in the gas phase at 2652, 2482, 2288, and 2120 A. The addition of gases capable of removing vibrational excitation enhances the quantum yield of isomerization indicating that the vibrationally ``hot'' isomer is formed in a rapid reaction. The intrinsic quantum yields of the isomerization process, obtained by extrapolating the observed yields to infinite pressure, are 0.0207±0.0013, 0.0463±0.0031, and 0.081±0.014 at 2652, 2482, and 2288 A, respectively. These results are in qualitative agreement with predictions of the correlation between the symmetry of the excited state and the direction of photochemical isomerization.

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