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.
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 close relationship between Raman spectroscopy and electronic spectroscopy is discussed in detail. It is found that information obtainable from these two fields are really complemental. Expressions for the contributions to the Raman scattering process from vibronic interactions and Condon effects are derived. The theoretical considerations are applied to calculate absolute Raman intensities of many diatomic molecules, to derive the selection rules of rotational Raman spectrum, and to interpret Raman spectra of organic crystals.
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.
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