The Infrared, Raman, Resonance Raman Spectra, and the Valence Force Field of the HfS3 Layer‐Type Compound

The infrared and Raman spectra (600 to 10 cm−1) of polycrystalline samples and of single crystals of HfS3 are investigated. A complete assignment is proposed and the frequencies of normal modes in HfS3, ZrS3, and TiS3 are compared. Resonance Raman spectra of HfS3 are recorded using a variety of Kr+, Ar+, and stilbene‐3 dye‐laser lines (647.1 to 431.2 nm) within the contour of the lowest allowed excitonic transitions. In agreement with previous studies on ZrS3, the unresolved excitation profiles are well accounted for by a Franck‐Condon scattering mechanism in which several modes and several interfering electronically excited states are involved. Finally, a valence force field with intrachain, interchain, and interlayer contributions is proposed: the potential energy distributions and mean square vibrational amplitudes are computed and the force‐constant values are compared in HfS3 and ZrS3 compounds. It is concluded that the lattice dynamics are governed by the two‐dimensional or layer‐type character of these MS3 systems.