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.
Force constants of planar symmetric XYn type molecules in the Cartesian space have been derived in terms of the vibrational frequencies. The force constants and normal coordinates of some planar XY3 molecules with available isotoptic data are worked out. Further study of infrared absorption spectra of square planar XY4 complex ions will be needed for the present normal coordinate analysis.
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 absorption spectrum of the lowest triplet state (T1*‐S0) of trans‐stilbene is observed between 14,000 and 18,000 cm−1 with a crystal four centimeters long, cooled to 4.2°.K. This transition is more intense (f=3×10−9) than the similar transition in anthracene, due to vibration‐induced spin‐orbital coupling. Vibrational structures in the spectrum are well resolved and seven frequencies are assigned to normal modes in the T1* state of trans‐stilbene. Exciton structures in crystal are not resolved.
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