Abstract
The development and increasing application of far-infrared spectroscopy has led to a corresponding need of sample-preparation techniques suitable for the far-infrared frequency range. With respect to solid-state samples, methods used for normal-infrared range spectra have been applied with some success to the far infrared. Thus, samples may be mulled with the usual mineral oils since such oils have good transmission properties throughout the far-infrared range. Pellets made of cesium iodide transmit very well down to 175 cm<sup>−1</sup>, and the method of preparation is essentially the same as for potassium bromide pellets. Interest in far-infrared spectra, however, often extends well below this frequency. A remarkably convenient matrix material with excellent transmission from 650 cm<sup>−1</sup> to at least 33 cm<sup>−1</sup> (low-frequency limit on the Beckman IR-11) is polyethylene. The polymer in powder form, to which has been added a small quantity of sample, can be melted at relatively mild temperatures and then recooled to form a pellet semitransparent in appearance. These pellets are tough and durable, do not absorb atmospheric moisture, and do not alter perceptibly even after long periods of time.
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