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Top Curr Chem (2003) 230:117–134 DOI 10.1007/b12405 Speciation and Thermodynamics of Sulfur Vapor Ralf Steudel1 · Yana Steudel1 · Ming Wah Wong2 1 Institut für Chemie, Technische Universität Berlin, 10623 Berlin, Germany E-mail: steudel@schwefel.chem.tu-berlin.de 2 Department of Chemistry, National University of Singapore, Science Drive 3, 117543 Singapore E-mail: chmwmw@nus.edu.sg Abstract Sulfur vapor at temperatures of between 200 and 1000 C consists of all molecules with 2–10 atoms, some of which exist as two or more isomers. Extensive mass spectromet- ric investigations and vapor pressure measurements provided reliable thermodynamic data for the various dissociation reactions S8Ð8/n Sn. Earlier quantum-chemical calculations yielded data partly in conflict with these experimental findings, but the most recent high- level ab initio MO and DFT calculations confirmed more or less the best experimental re- sults. These theoretical data may now be considered as the most trustworthy. At low tem- peratures S8, S7, and S6 are dominating in saturated sulfur vapor, the concentration of S4 passes through a maximum at 900 K, S3 is always more abundant than S4, and S2 is the dom- inating species above 1100 K. The S4 molecule is of cis-planar geometry but under non- equilibrium conditions the trans-planar isomer has also been observed. Triplet chain mole- cules Sn·· as well as branched rings Sn=S and other isomers are too unstable to contribute more than 1% in each group to the equilibrium vapor composition at any temperature. Keywords Sulfur clusters · Quantum-chemical calculations · Stability · Isomers · Spectra 1 Introduction................................... 118 2 SulfurVapor................................... 118 2.1 General ...................................... 118 2.2 MassSpectrometry............................... 119 2.3 PressureandDensityMeasurements.................... 121 2.4 MoreMassSpectrometry........................... 122 2.5 VibrationalSpectra............................... 122 2.6 UV-VisSpectra ................................. 124 2.7 Quantum-ChemicalCalculations...................... 125 3 Summary..................................... 132 References........................................ 132 Springer-Verlag Berlin Heidelberg 2003PDF Image | Topics in Current Chemistry
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