A 35° cesium iodide prism has been installed in a Perkin-Elmer 12C infrared spectrometer. After the stray radiation had been reduced by filters, it was possible to observe infrared radiation at wavelengths as long as 54µ. The spectrometer was calibrated by the identification of rotational lines of atmospheric water by using the known grating values. The single-pass and the Walsh double-pass systems were compared and their advantages noted. The transmittances of crystals of CsBr, TlBr-I, CsI, and of films of polystyrene and polyethylene have been measured. In addition, the absorption spectrum of three halomethanes and three halobenzenes has also been observed. Prism spectrometry from 24 to 54µ with a CsI prism is handled by the same methods as those used with a CsBr prism. The spectra of several molecules are given for the region from 25 to 50µ.
NICOLO ACQUISTA and EARLE K. PLYLER, "Infrared Measurements with a Cesium Iodide Prism," J. Opt. Soc. Am. 43, 977-979 (1953)