EXPERIMENTAL MOLECULAR HYPERPOLARIZABILITIES FROM VIBRATIONAL-SPECTRAIN SYSTEMS WITH LARGE ELECTRON-PHONON COUPLING

Experimental data are presented and discussed on the relaxation contri bution (beta(r) and gamma(r)) to first- and second-order molecular hyp erpolarizabilities of classes of polyconjugated organic materials. The se data are obtained from the measure of classical vibrational observa bles, i.e., vibrational frequencies, infrared intensities and Raman cr oss sections. It turns out that the values of beta(r) and gamma(r) are very similar (both in values and trends) to the electronic molecular hyperpolarizabilities beta and gamma obtained from traditional direct experiments. It is concluded that for the molecular systems considered , beta(r) and gamma(r) may be a good estimate of static, non-resonant beta and gamma. The justification for such conclusions is that in poly conjugated systems very large electron-phonon coupling takes place suc h that vibrational displacements are strictly related to and cannot be separated from electronic excitations.