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Cell Design for the Measurement of Transmission Spectra of Liquids at Very Long Infrared Wavelengths
Volume 23, Number 6 (Dec. 1969) Page 620-621
Measurements of the infrared transmission spectra of solids and liquids at moderate to high resolution are often troubled by undesirable interference effects caused by multiple internal reflection in parallel-sided materials (commonly known as "channel spectra"), which usually become increasingly pronounced at longer wavelengths. The purpose of this communication is to describe how a commercial vacuum-tight liquid cell may be modified to minimize such interference effects arising both in the cell windows and in the liquid cavity, and to present liquid transmission spectra recorded in the range 7-70 cm−1 using such a cell in conjunction with a small commercial lamellar grating interferometer. Briefly, the amplitude of "channel spectra" observed in the transmission spectrum of a material layer depends directly upon the transparency of the medium, the effective reflection, co-efficient at the material boundaries, and the degree of parallelism of the layer thickness compared to the ir wavelength of observation.