Raman and far-infrared spectra of proustite (Ag3AsS3) and pyrargyrite (Ag3SbS3)

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Abstract
The polarized Raman spectra of large (1 cm × 1 cm diameter) single crystal specimens of proustite (Ag3AsS3) and pyrargyrite (Ag3SbS3) have been obtained The number of irreducible representations of the unit cell, C3μ6 factor group, was calculated and the nineteen fundamental Raman and infrared-active modes (K ≈ 0) were accounted for in both materials. The far-infrared spectra were obtained from powder samples.The vibrational modes were characterized qualitatively via symmetry coordinates calculated from internal coordinates of the unit cell. It is concluded that the low frequency A1 mode (37 cm-1) seen in both materials involves essentially torsional motion of the AsS3 ≡ and SbS3 ≡ pyramids about the c-axis.