Lattice Vibrations and Interatomic Forces in LiInS2

Infrared reflectivity spectra of LiInS₂ are measured at room temperature in the wave-number range from 180 to 4000 cm⁻¹. The parameters of four optical modes are determined by a dispersion analysis of the spectra. From the interatomic force constants determined from the sphalerite-like modes in the lattice vibration spectrum it follows that the Li–S bond is considerably weaker than the In S bond.