POLARIZED RESONANCE RAMAN-SPECTRA OF AN ORIENTED DIPHENYLPOLYENE

Measurements of polarized Raman intensities of partially oriented molecules were shown to be useful for obtaining information about the components of the scattering tensor and the degree of orientation in anisotropic samples. The polarized resonance Raman (RR) spectra of all‐trans‐1,14‐diphenyltetradecaheptaene (DPTH) incorporated in a stretched polyethylene film were studied. The DPTH molecules are highly oriented in the polymer matrix with their longitudinal axis in the direction of stretching. The different components of the scattering tensor for the totally symmetric vibrations of DPTH were determined in the case of resonance excitation. It was found that the diagonal element αzz (z is defined along the polyene chain) gives the largest contribution to the RR intensity. However, the two off‐diagonal elements αzy and αyz also contribute significantly and have different magnitudes. The physical origin of these off‐diagonal elements and of the asymmetry of the scattering tensor are discussed in terms of the vibronic coupling theory. Copyright © 1979 Heyden & Son Ltd.