Use of the Curtis-Godson approximation in calculations of radiant heating by inhomogeneous hot gases

Curtis-Gordon approximation in calculations of radiant heating by inhomogeneous hot gase

ERRORS IN SPECTRAL ABSORPTION MEASUREMENTS DUE TO ABSORBING SPECIES IN THE ATMOSPHERE∗ATMOSPHERE^{*}

$^{1}$H. Sakei and F Stauffer, J. Opt. Soc. Am. 53, 507, MA16 (1963). $^{*}$This work was supported in part by NASA Lewis Research Center and by the Advanced Research Projects Agency. $^{1}$D. E. Burch, D. Gryvnak, and D Williams, Report No. II, Contract AF 19(604)-2633, pp. 5-9. AFCRL-Author Institution: The Warner \& Swasey Company“The accuracy of spectrosopic absorptance measurements can be seriously affected by the presence of absorbing species in the atmosphere anywhere in the optical train The error is due to the baud-pass nature of a monochromator and is just as severe when a double beam spectrometer is $used^{1}$ as when a single-beam spectrometer is used. Using the method of $Sakei^{2}$ for the calculation of the integrated absorptance at a pair of over- absorption lapping absorption lines, we have calculated the error in the measured integrated absorptance of a sample gas which contains $H_{2}O$ or $CO_{2}$. A number of experimentally important cases have been considered with the object of correcting the measured absorptance. The calculations are compared with experiment. 255 (1960).

EXPERIMENTS ON THE APPLICABILITY OF THE BEER--LAMBERT ABSORPTION LAW TO THE SPECTRA HOT CO2CO_{2} AND H2O∗H_{2}O^{*}

$^{*}$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.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

STRENGTHS AND WIDTHS OF PRESSURE-BROADENED HCll INFRARED LINES∗LINES^{*}

$^{*}$This research was supported by the United States Air Force through the Air Force Office of Scientific Research of the Air Research and Development Command under Contract No. AF18(600) 986. $^{1}$Kaplan and Eggers, J, Chem. Phys. 85, 876 (1956).Author Institution: Department of Physics, University of Pittsburgh“As part of an investigation of the various aspects of the pressure broadening of infrared absorption lines, we have undertaken the measurement of the line strengths and widths of several of the P-branch lines of the fundamental vibration-rotation band of HCl. The value here obtained for the band absorption coefficient, $S^{o}_{1, 0}$, is $143 cm^{-1}$ $atm^{-1}$. This is based on a line strength for the P-1 line, $S^{o}_{P 1}$ of $6.60 cm^{-2}$ $atm^{-2}$ at $300^{\circ} K$. The line width of the P-1 line when broadened by nitrogen is $\alpha^{o}_{{P}-1}=.12$ $cm^{-1}$ $atm^{-1}$ at $300^{\circ} K$. One of the favorable aspects of the present method is the use of a single large absorption cell into which are introduced easily reproducible mixtures of gases under moderute pressures. The resulting lines are large and easily planimetered. The resulting equivalent widths are treated in a manner indicated by the following equation: $\frac{{W}^{35}\alpha^{37}}{{W}^{37}\alpha^{35}}=\frac{{f}(8{x}^{37})}{{f}({x}^{37})}$ where ${x}=\frac{{SL}}{2\pi\alpha}, \beta=\frac{{x}^{35}}{{x}^{37}}$ and the function f(x) is well known and $tabulated^{1}$. S is the line absorption coefficient, L is the optical path length, and $\alpha$ is the line half-width produced by relatively large nitrogen pressures. The superscripts refer to the two isotopic lines of HCL. To obtain a large value of $\beta$, the less abundant isotope at very low HCL pressure and high ($\sim$ one atmosphere) $N_{2}$ pressure is used in one half of the experiment, while the more abundant isotope at higher HCL pressure and low ($\sim \frac{1}{6}$ atmosphere) $N_{2}$ pressure is used in the second half. It may be noted that this method is not inherently dependent on the presence of isotopes.