EXPERIMENTS ON THE APPLICABILITY OF THE BEER--LAMBERT ABSORPTION LAW TO THE SPECTRA HOT $CO_{2}$ AND $H_{2}O^{*}$
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Date
1961
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Ohio State University
Abstract
Although it has long been recognized that experimental measurement of the absorption spectra of gases at room temperature depart substantially from exponential (or Beer-Lambert) law of $absorption,^{1}$ recent experiment on $CO_{2}, H_{2}O$, and mixtures of $CO_{2}$ and $H_{2}O$ heated in an electric $oven^{2, \ 2}$, and on $CO_{2}-N_{2}$ mixtures by a $shockwave^{4}$ have indicated that the exponential law does apply to the spectral absorption of hot gases. However, a large discrepancy between the absorption coefficient at $4.4 \mu$ calculated form the shock tube measurement and the coefficient calculated form the data on $CO_{2}$ heated in the oven has led to a renewed interest in the problem of the absorption law for heated gases. The results of a series of measurements on the absorption of pure $CO_{2}$ an of $CO_{2}$ mixed with $N_{2}$ and He will be presented. Granting that a complete understanding of the experimental results may not be at hand, it is clear that the usefulness of absorption coefficients form such measurements is severely circumscribed (even when a plot of the negative logarithm of the transmittance-vs-optical depth is linear). In particular, it is risky to use measured absorption coefficients for extrapolation to lesser or greater optical depths than those used for the determination of the absorption coefficients.
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$^{*}$This research was supported by the U.S. Air Force through the Geophysics Research Directorate, Bed ford. Mass. $^{1}$K. Angstrom, Phys. Rev. t. 597 (1892). $^{2}$R. H. Tourin, J. Opt. Soc. Am. 51, 175 (1961). $^{3}$R. H. Tourin, J. Opt. Soc. Am., in press. $^{4}$M. Steinberg, J. Chem. Phys., in press.
Author Institution: The Warner \& Swasey Co., Control inst, Div.
Author Institution: The Warner \& Swasey Co., Control inst, Div.