1969 Volume 42 Issue 12 Pages 3390-3393
Cyclohexane-1,4-dione is an aliphatic ketone with two carbonyl groups. The absorption due to the n–π* transition of the carbonyl group extends from the 30000 cm−1 to the 42000 cm−1region. The transition is symmetrically forbidden and is assigned to the A1-A2 transition in the C2v system. The spectra in the crystal and in a solution of EPA at 77°K show only prominent carbonyl stretching vibrations. The polarized single crystal absorption spectra at 4.2°K are composed of many sharp lines; the vibrational structures are analyzed in detail. The 0–0 transition is observed at 31408 cm−1; the distinct basic frequencies of the excited state are 1096, 790, 557, 375, 247, and 122 cm−1, while the lattice vibrations are 61, 32, and 22 cm−1. The transition is explained by the vibronic coupling mechanism, assuming the C2v symmetry for the carbonyl group. Two different types of progressions are noticed; one is induced by the out-of-plane b2-type vibration, while the other is allowed by the a2-type vibration. The dichroic properties of the crystal spectra allowed the assignment of the vibrational modes. These vibrations are compared with the infrared and Raman spectral data.
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