Infra-red absorption spectrum of tetra-deuteroethylene

Abstract

The ethylene molecule possesses twelve fundamental modes of vibration of which seven have been identified with certainty from its infra-red absorption and Raman spectra. The remainder have been tentatively assigned in different ways by different authors, and much uncertainty exists regarding their true values. The present investigation was undertaken with a view to obtaining new information on a closely related spectrum which might enable one to discriminate between those assignments. An equally important reason was that the ethylene molecule has been made the subject of many theoretical investigations in attempts to find a suitable representation for the force field within a polyatomic molecule. Such theories may best be tested by seeing how closely they predict the frequencies of the isotopic molecule. In some cases it is necessary to know a few of the frequencies of the isotopic molecule, in addition to those of the normal molecule, to obtain all the constants of the force field. The remaining isotopic frequencies may then be predicted and their verification used as a test. This work was made possible largely through the kind co-operation of Professor de Hemptinne of the University of Louvain, who supplied us with the specimen of C 2 D 4 used (de Hemptinne, Jungers and Delfosse 1938). He and his colleagues were simultaneously investigating the Raman spectra of the various deuteroethylenes with a similar object in view. The sample we employed was estimated to have a light hydrogen content of not more than 10%.