Raman Spectrometric Study of the Composition of Sulfur Vapor at Temperatures up to 700°C

Abstract

AbstractSulfur vapor has been investigated by Raman spectroscopy in a wide temperature and pressure range (300 to 900°C, 0.05 to 0.5 MPa for overheated vapor and 0.007 to 1.65 MPa for saturated vapor). At least eight different species have been observed through their characteristic Raman lines. Well separated Raman lines have been selected for the observation of the change in vapor composition with temperature: symmetrical bending modes for the cyclic species S8, S7, and S6 and stretching modes for the chain‐like species S3 and S2. There are indications for the presence of two conformational isomers of S4, and in addition a new species has been discovered by its resonance Raman line at 635 cm−1 which is tentatively assigned to chain‐like molecules Sn (n > 4) of helical conformation. Several relationships between the thermodynamic properties of the vapor and the Raman measurements are proposed, e.g., the determination of the temperature at which the molar fraction xi is maximum for the overheated vapor at constant pressure; estimation of the xi/x8 ratios using solution measurements of the Raman cross section for the molecules S8, S7, S6. A careful comparison of these results with the values deduced from Rau's model results in good agreement for the behavior of most of the species apart from S7 which is underestimated in Rau's model. S7 is the dominating species in saturated sulfur vapor above 600 K until S2 takes over at ca. 1000 K.