First- and second-order Raman spectra of galena (PbS)

Raman spectra of cleaved, millimeter-sized single crystals of mineral galena (PbS) have been measured between 100 and 1200 cm−1 over the temperature range 80 to 373 K. Three low wave number bands are observed which can be reconciled with the results of earlier reports. However, changes in the peak wave numbers and in the relative intensities of these bands in response to changes in temperature do not conform with previous assignments for the observed bands. Detailed assignments are proposed which are based on resonance Raman processes. The observed bands are assigned to forbidden longitudinal optical excitations, which are allowed under resonance conditions by a Fröhlich interaction mechanism, and two-phonon excitations.