The nature of scattering centers in resonance stimulated Raman scattering by dyes and shape of the emitted spectra

An investigation was made of the resonance stimulated Raman scattering (RSTRS) spectra of the polymethine dye 3, 3'-diethylthiatricarbocyanine iodide when the pump frequency was scanned along the long-wavelength edge of the absorption band. A change in the relative intensities of the 505 and 510 cm^–1 RSTRS lines was observed near the purely electronic transition. The character of this change suggests that this line may be assigned to scattering by unexcited dye molecules. The mechanism for enhancement of RSTRS and the shape of the bands in the spectra due to interference between two types of secondary radiation—RSTRS and stimulated luminescence—are discussed. Experimental data illustrating the different cases of formation of the RSTRS line profile are discussed. An analysis is made of the criteria that can be used to determine the electronic state in which RSTRS takes place.