Investigations in the infra-red region of the spectrum. Part V.— The absorption spectrum of carbonyl sulphide

Abstract

The symmetrical linear structure of both carbon dioxide and carbon disulphide is now well established. Recent developments in theory make it highly probable that a complete explanation of the Raman and infra-red spectra of these substances, with the concomitant selection rules, will shortly be available. It is in the meantime of consequence to examine the absorption spectrum of carbonyl sulphide, since the chemical and external physical properties of this molecule are intermediate to those of the other two, though the lack of symmetry in its structure predicts more complex intramolecular relationships. No previous determination of this spectrum appears to have been made. Experimental . Carbonyl sulphide was prepared by dropping sulphuric acid (5 parts of acid to 4 of water by volume) on to potassium thiocyanate in a flask maintained at 21° C. by means of a water bath. The chief impurities generated in the reaction are carbon disulphide, carbon dioxide, and carbon monoxide* ; the gaseous product was led firstly through a trap immersed in a freezing mixture of salt and ice, secondly through a bubbler containing a 33 per cent, solution of potassium hydroxide, thirdly through a tube of active charcoal, fourthly through calcium chloride, and finally, through a trap immersed in a saturated solution of carbon dioxide snow in acetone, to the fume cupboard v en t; glass to glass seals were used throughout. The traps and tubes removed in succession the major portion of the carbon disulphide, the carbon dioxide, the remaining carbon disulphide, and the water vapour ; carbonyl sulphide boils at —50° C. and was condensed in the last trap at a temperature of —78°, any carbon monoxide passing on unabsorbed. When sufficient of the required substance had been collected, the trap was disconnected from the generating apparatus and connected to the absorption tube system, where the gas was transferred to an evacuated aspirator and stored over phosphoric oxide. The aspirator was totally enclosed to obviate possible decomposition of the carbonyl sulphide by light.