A Recording Double-Beam Infra-Red Spectrophotometer

A recording infra-red spectrophotometer is described which, by the automatic balancing of two beams of radiation from the same source, is designed to eliminate variations in the spectrum caused by atmospheric absorption, changes in source radiation intensity, and drifts in the electronic amplification. The infra-red absorption spectrum of any chemical compound can thus be recorded directly as percentage of radiation absorbed versus wave-length. If in solution, the solvent can be placed in the other beam, and the absorption due to the compound alone can thus be ascertained. The optical system is basically similar to that of the instrument by Baird Associates. Schwartz thermopile type F 1440 by A. Hilger Ltd. is used instead of a bolometer. Slits of a new type of design are used, and a d.c. servo system is employed for the recorder and light balancing mechanism. The spectral region covered is from 2 to 16 μ, and recording time is from 12 min. upwards. General details of the optical, mechanical and electronic construction are given. The performance data and examples of the applications of this instrument will be published later.