The electronic structures of trans‐ and cis‐stilbene are calculated using Pariser and Parr's semiempirical method. The resonance integrals are adjusted so as to give the best agreement with the spectroscopic data. In addition, the potential surfaces of various excited states in stilbene during its isomerization process are calculated. Our results differ significently from those of Borrell and Greenwood2) who did not realized the importance of a doubly excited singlet state to the potential surface of the ground state of stilbene. Our improved potential surfaces suggests mechanism of various radiationless leading to photoisomerization and sensitized isomerization.
The polarized Raman spectra of naphthalene single crystal are recorded with a laser Raman spectrometer. Relative intensites of Raman lines in various polarizations are accurately measured by photon‐counting technique. All the strong lines are polarized in the c′c′ and bb polarizations, and the polarization data alone are not sufficient to decide the symmetry of a Raman active vibration. The oriented gas model is found not adequate to fully understand the results. The polarization data have to be interpreted in terms of the electronic spectrum of naphthalene.
Though the spectra in polyphenyIs are often broad and structureIess, the general pattern of these spectr> is very similar to those in polyacene series. The systematic behavior of the a, p , and p bands i n BP-poIyphenyIs can be -explained in terms of simple MO theory with the first order configuration interaction. . The behavior of the p and B bands can also be approximateIy calculated by straightforward exciton theory. The usefuhess of the exciton theory is best demonstrated in the case of m-poIyphenyIs.Platt's notations' are entirely irrelevant since polyphenyls cannot be treated as distorted cyclic polyenes.
The Raman spectra of powdered biphenyl, p‐terphenyl, and p‐quaterphenyl are compared with each other and also with the Raman spectrum of benzene. Most Raman lines in polyphenyls can be considered as derived from normal vibrations in benzene. The intense lines are thus assigned and the correlations between them are established.
The Raman spectra of the p‐polyphenyls: benzene, biphenyl, p‐terphenyl, and p‐quaterphenyl, are compared with their electronic spectra. The relative intensity of the double bond stretching mode around 1600 Kaisers to that of the breathing mode around 1000K increases steadily when the phenyl chain is lengthened. This intensity ratio can be calculated using our theory proposed previously.1 The results are in very good agreement with the experimental observations
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