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1965-M-04.jpg 202.3Kb JPEG image Thumbnail of FIRST AND SECOND TRIPLETS OF SOLID BENZENE.

Creators: Bernstein, E. R.; Colson, S. D.
Issue Date: 1965
Publisher: Ohio State University
Abstract: Absorption spectra have been taken of the $O_{2}$-perturbed first $(^{3}B_{10})$ and second $(^{3}E_{10})$ triplets of solid benzene at $4.2^{\circ}K$. Spectra of both $C_{6}H_{6}$ and $C_{3}D_{6}$ were obtained. The (0-0) bands of the first triplet occur at $29,674 cm^{-1} \pm 25 cm^{-1}$ for $C_{6}H_{6}$ and $29,851 cm^{-1} \pm 25 cm^{-1}$ for $C_{6}D_{6}$. For the second triplet they lie at $36,560 cm^{-1} \pm 50 cm^{-1}$ for $C_{6}H_{6}$ and $36,784 cm^{-1} \pm 50 cm^{-1}$ for $C_{6}D_{6}$. The result for the first triplet of $C_{6}H_{6}$ compares very favorably with Evans' gas phase $O_{2}$-perturbed spectrum. It is also in satisfactory agreement with Nieman's accurate phosphorescence measurements on isotopic mixed crystals of benzene which place the $C_{6}H_{6} (0-0)$ band position in the crystal at $29,657.1 cm^{-1}$. The position of the second triplet lies about $3,000 cm^{-1}$ above that given by the Pariser-Parr calculation. Many precautions were taken to eliminate the possibility of misidentification of the second triplet. The rather broad structure obtained by the $O_{2}$ perturbation technique does not allow a detailed study of this interesting state. Crystals, up to 5 cm in length, of very highly purified $C_{6}H_{6}$ and $C_{6}H_{6}$ were also studied at $4.2^{\circ}K$ to ascertain if the single-triplet absorptions could be seen in the absence of a perturbation. These experiments, however, were somewhat disappointing. The long crystals showed some sharp and some broad $(\Delta v \approx 150 cm^{-1})$ absorptions starting at $36,954 \pm 50 cm^{-1}$ in $C_{6}H_{6}$ and at $37,147 \pm 50 cm^{-1}$ in $C_{6}D_{6}$. Nothing except weak impurity absorption was seen at lower energy. The broad absorptions correlate reasonably well with the features assigned to the second triplet in the $O_{2}$ perturbation experiments. The first triplet is too weak to be observed in the long crystal experiments.
Description: Author Institution: Department of Chemistry, California Institute of Technology
Other Identifiers: 1965-M-4
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