Fine Structure in the Absorption Spectrum of Alpha-MnS

Fine structures in absorption spectra of α-MnS single crystals are investigated at low temperatures. The sharp and temperature-independent band C : 6 A 1 →[ 4 A 1 , 4 E ] has five components, which can be explained in terms of covalency, descent of the crystal field symmetry and phonon-assisted transitions. In the visible and near-ultraviolet regions, five absorption bands are observed. The calculated band positions are fit for the observed bands at 4.2°K with the covalency parameter e =0.17, the Racah parameters B =808 cm -1 , C =3751 cm -1 and the crystal field strength D q =1025 cm -1 .