Resonant-Raman-scattering studies of disorder in solution-cast polydiacetylene films

The disorder in polydiacetylene films cast from solution is studied by Raman scattering under preresonance and resonance conditions in both Stokes and anti-Stokes configurations. The disorder-induced inhomogeneities in the exciton energy levels and the strongly coupled vibrations cause strong dispersion of the C = C and C = C stretching frequencies with the laser excitation photon energy, surprisingly similar to that of trans-polyacetylene. We show, however, that the complete inhomogeneously broadened phonon distribution is revealed when the excitation is not in resonance. In addition to the excitation resonance, resonances associated with the Stokes and anti-Stokes emission beams strongly affect the measured Raman profiles.