The quantitative determination of atmospheric gases by infra-red spectroscopic methods I. Laboratory determination of the absorption of the 7.8 and 8.6 μ bands of nitrous oxide with dry air as a foreign gas

Abstract

New data on the effect of amount of gas, pressure of dry air, and temperature, upon the 7.8 and 8.6 μ bands of nitrous oxide, have been analyzed in an attempt to find all the fundamental information required in order to use the 7.8 μ band for the quantitative determination of atmospheric nitrous oxide from telluric spectra. By taking rather more care than has been usual in the measurements of intensity the following conclusions can be reached: (1) It is possible to measure band intensities with a reasonable degree of accuracy. The results obtained at temperatures near 300°K are: ∫ 7.8 μ k v dv ═ 4.02 ( ± 0.08) x 10 15 c. /sec. per g. cm. -2 , ∫ 8.6 μ k v dv ═ 1.66 ( ± 0.03) x 10 14 c. /sec. per g. cm. -2 . (2) The line broadening in a range of pressures, extending from 1 cm. of mercury to 1 atm. of dry air, is caused by a collision process. (3) In this range of pressures, the shape of the wings of absorption lines is well represented by the Lorentz form. (4) The line width at 1 atm. pressure is the same for the 7.8, 8.6 and the 17 μ bands, and its most probable value is given by 2 α L ═ 0.314 ( ± 0.015) cm. -1 . (5) At pressures below 5 mm. of mercury, Doppler broadening becomes predominant. (6) The effect of temperature upon absorption agrees with theoretical prediction, excepting the dependence of collision diameter upon temperature.