Spectra of the 4.7-µ band of CO were obtained after a beam of continuous radiation had passed through two cells containing mixtures of CO and N2. The total pressure and CO concentration of the first cell were adjusted so that the absorption by it lay in the “square-root region” where the absorption is approximately proportional to the square root of the total pressure and CO concentration. Spectra were then obtained as the total pressure and CO concentration in the other cell were varied over a wide range. An empirical expression was found relating the total absorption to the pressures and absorber concentrations of the two cells.
DAVID A. GRYVNAK and JOHN H. SHAW, "Study of the Total Absorption near 4.7 µ by Two Samples of CO as their Total Pressures and CO Concentrations were Independently Varied," J. Opt. Soc. Am. 52, 539-542 (1962)