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“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.”


$^{*}$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