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Abstract
It appears that many people are under the impression that it is not possible to record meaningful infrared spectra of samples which are almost “black,” i.e., samples which cause the radiation reaching the instrument's detector to be less than a few per cent of the radiation of the unattenuated source. We have, however, been working quite successfully with samples of this nature for a number of years, using commercially available instruments to record transmission and emission spectra with signals of very low intensity. It consequently seems useful to point out that unmodified, commercial research-quality spectrophotometers are capable of better performance than is generally realized. The purpose of this review is, then, to show what can be studied under such poor signal conditions and how this is done, and to describe some of the difficulties and effects that may be encountered.