Forbidden chemistry of sulfur in the gas phase


Paul Marshall, University of North Texas, Department of Chemistry, 1155 Union Circle #305070, Denton, Texas 76203-5017, USA


Nitrogen oxides, sulfuric acid and particulates are undesirable products of combustion. Sulfur in fuels can have a strong influence on formation of these pollutants, but the detailed mechanisms are not well understood. The kinetics of elementary reactions of radicals in the gas-phase are isolated in experiments using pulsed UV laser photolysis of precursors combined with time-resolved fluorescence detection. Ab initio computational modeling helps interpret the measurements involving sulfur-containing species including atomic sulfur, H2S, SO2, CS2 and alkali metal sulfates. In many cases these processes are forbidden by conservation of spin, or appear to be entropically unfavorable or too fast according to conventional guidelines.