On account of the relatively small amount of energy emitted from sources in the wave-length region beyond 15µ, stray energy of short wave-length from the source becomes a considerable proportion of the energy indicated by the detecting system. By use of a reflection filter of LiF, this stray radiation is greatly reduced.
The infra-red spectra of cyclopentane, methylcyclopentane, ethylcyclopentane, and isopropylcyclopentane have been measured and each has a characteristic spectrum, which can be used in analysis.
Also, the spectra of cyclohexane, methylcyclohexane, ethylcyclohexane, and secondary butylcyclohexane have been measured and a number of bands which are characteristic of these substances have been observed.
EARLE K. PLYLER, "Infra-Red Spectrometry from 15 to 25µ," J. Opt. Soc. Am. 37, 746-753 (1947)