Microscopic and imaging Raman scattering study of PbS and its photo-oxidation products

Spatially resolved molecular information on galena (PbS) crystals was obtai ned by microspectrometric Raman mapping through a high numerical aperture o bjective. Different experimental conditions were used: excitation wavelengt h, excitation power, crystal size and temperature, Spatially guided analysi s was obtained from the spectra recorded in the point-by-point microprobe m apping mode with 1 mum spacing between the points. Multivariate data proces sing yielded the typical spectra of PbS and its degradation products. The R aman features of PbS were found to be weak under non-damaging excitation co nditions. The laser-damaging effect generates complete and irreversible oxi dation of PbS to alpha -PbO for particles of size of the order of micrometr es, For larger PbS crystals, several lead oxysulphates including 4PbO . PbS O4 and 3PbO . PbSO4 were located in the vicinity of the illuminated spot by Raman mapping, Copyright (C) 2000 John Whey & Sons, Ltd.