The spectra of flames containing oxides of sulphur

Abstract

The spectra and characteristics of hydrocarbon and related flames containing small amounts of SO 2 and SO 3 have been studied; observations have been made with a view to elucidating the mechanism of carbon formation in flames. Band systems due to S 2 , SO, CS and SH occur; this is the first record of the SH band in emission. The mechanism of the formation of these radicals is discussed. The outer cones of flames containing SO 2 show strong ultra-violet continuous emission, and this is provisionally attributed to direct association between SO 2 and atomic oxygen to give SO 3 . Failure to obtain luminous reaction between SO 2 and atomic oxygen in a discharge tube at room temperature indicates that this reaction requires an activation energy. The formation of SO 3 cannot be used as a quantitative test for atomic oxygen in flames. SO 3 increases carbon deposition in hydrocarbon flames and it is considered that it can induce chain reactions leading to the polymerization and decomposition of hydrocarbons. These chain reactions are maintained by free radicals which may be produced either by direct reaction of sulphur trioxide with hydrocarbons or indirectly through the formation of peroxides. SO 2 and H 2 S, which reduce carbon deposition, either inhibit the chain processes or remove carbon as soon as it is formed.