Total Absorptance by Nitrous Oxide Bands in the Infrared

Abstract

Instrumentation and experimental techniques employed for the determination of the total absorptance ∫A(ν)dν of the bands of various atmospheric gases are described. The total absorptances of the 2563, 2461, 2224, 1285, 1167, 692, and 589 cm⁻¹ bands of pure N₂O and N₂O mixed with N₂ have been determined as a function of absorber concentration w and equivalent pressure P_e which involves the partial pressures of the two gases. The results are given in graphical form. In general, it is found that in situations in which existing theory predicts absorptance proportional to the square roots of pressure and absorber concentration, the total absorptance is indeed nearly proportional to the square root of absorber concentration but not to the square root of the pressure; for the 2224 cm⁻¹ band, ∫A(ν)dν ∝ P_e^0.37. In addition to graphical presentation of results, it is possible to express ∫A(ν)dν in terms of w and P_e by means of empirical equations applicable to certain definite ranges of the variables; the validity and the limitations of such empirical equations are discussed. For samples for which the product of the absorption coefficient k(ν) and the absorber concentration is much less than unity for all frequencies in an absorption band, it is possible to measure the band intensity or band strength ∫k(ν)dν. Values of band intensity for the 2563, 2461, 2224, 1167, and 589 cm⁻¹ N₂O bands are listed and compared with values previously reported by others.