Infra-red investigations of molecular structure.-Part I. Apparatus and technique

It is the aim of this series of papers to extend knowledge of the structure of molecules by work in the infra-red. There are three obvious lines of development. The first is the study of the spectra of diatomic gases and the deductions which follow according to the classical quantum theory ; this has already been done with success by Imes (Sleator, Astropys. J.,' vol. 48, p. 125 (1918); Imes,ibid ., vol. 50, p. 251 (1919)) for the hydrogen halides. Comparisons will be made of the molecular constants from the infra-red bands with those obtained from electronic band spectra. As a second development there is the use of the infra-red results in the light of the newer quantum theory. Dennison's prediction ( 'Phys. Rev.,' vol. 31, p. 503 (1928)) of the shape of absorption bands needs confirmation by experiment ; and, if absolute intensities of absorption bands can be measured, the wave-mechanics is ready with an interpretation. Thirdly, the problems offered by triatomic molecules will be attempted. papers on the subject. Their work has removed most of the uncertainty which hinders such researches as this; but sines they do not discuss the use of gratings, and since we have found by experience that it is impossible to make a technique too clear, it has seemed desirable that the construction and use of an instrument should be described.