Electronic, vibrational and resonance Raman spectra of the layered semiconducting compound NbS3

The electronic (900–250 nm), infrared and Raman (600–10 cm−1) spectra of polycrystalline samples of NbS3 were investigated. A complete vibrational assignment is proposed and the band wavenumbers are compared for NbS3 and the related ZrS3 and NbS2Cl2. All the assignments have been checked by a complete valence force field calculation including intrachain, interchain and interlayer contributions. The potential energy distributions and mean square vibrational amplitudes so calculated and the values of force constants are in agreement with the two‐dimensional character of the lattice dynamics in NbS3. In addition, an extensive resonance Raman study has been performed using various exciting radiations in the visible (676.4–457.9 nm) and near‐UV regions (363.8 and 351.1 nm). The experimental unresolved Raman excitation profiles in the contour of two low‐energy electronic transitions (λmax≈︁ 600 and 560 nm) exhibit interesting interference and exact resonance effects depending on the nature of the vibration. Taking account of multi‐state interference phenomena and inhomogeneous broadening effects, these profiles compare well with the computed ones on the assumption of weakly displaced oscillators. This allows conclusions to be drawn about the scattering mechanisms and the nature of the first electronic excited states.