The volume of enclosed gas samples has been subjected to sinusoidal variation at a frequency of 8 cps; this volume modulation cycle is approximately adiabatic and involves temperature variations of several hundred degrees. Several emission bands of nitrous oxide in the spectral region between 3000 cm-1 and 1000 cm-1 have been investigated as a function of compression ratio for samples of pure nitrous oxide, nitrous oxide diluted with argon, and nitrousoxide diluted with various argon-nitrogen mixtures. Emission near the centers of strong absorption bands is that to be expected from a temperature-modulated blackbody provided the absorber concentration is sufficiently great to give complete absorption near the band center. For weaker bands and for strong bands with low values of absorber concentration, the effects produced by absorber concentration modulation and pressure modulation are superimposed on the effects attributable to temperature modulation. All observed effects can be interpreted on a semiquantitative basis in terms of an adiabatic modulation process.
RICHARD R. PATTY and DUDLEY WILLIAMS, "Infrared Emission from a Pressure-Modulated Gas," J. Opt. Soc. Am. 52, 543-544 (1962)