Spectrum of the afterglow of sulphur dioxide

Abstract

Following a previous investigation of the afterglow of carbon dioxide it was decided to examine sulpur dioxide under similar conditions of experiment. An afterglow of considerable intensity and duration had, in fact, already been noted by Professors Sir J. J. and G. P. Thomson as occurring when sulphur dioxide was excited in a ring discharge, but no observations on its spectrum appear to have been recorded. Strutt has recorded an afterglow when ozone is passed over sulphur, but no glow was recorded with sulphur dioxide. The spectrum yielded by SO 2 in vacuum tubes varies greatly according to the conditions of excitation. With sufficiently powerful condensed discharges and a rather low pressure of the gas the molecules are dissociated into atoms and the spectrum consists of lines of oxygen and sulphur. With uncondensed discharges of moderate intensity and a suitable pressure of gas, the spectrum shows a strong system of bands degraded to the red which have been analysed by Henry and Wolff and attributed to the diatomic molecule SO; these bands are most intense in the region λ 2442 to λ 3941. Still weaker excitation yields an entirely different system of bands extending from the blue to about λ 2000, and there is evidence that these bands are due to undissociated molecules of SO 2 . The absorption of SO 2 is characterized by a large number of bands, which are most intense in the region λ 2800 to 3150. Owing to the continuous spectrum emitted by the gas during electrical excitation, this absorption may appear superposed on the emission spectrum in some forms of discharge tube. Recently Lotmar has reported on a band system excited in SO 2 by fluorescence.