Infrared Absorption by Carbon Monoxide at High Temperature

Abstract

The absorption of infrared radiation by carbon monoxide has been measured at wavelengths of 4.60, 4.67, and 4.72 μ for temperatures from 1160° to 2300°K. The test gas was heated to the desired temperatures by shock compression. The carbon monoxide optical density varied from 4 to 11 atm-cm; total gas pressures ranged from 1.40 to 3.60 atm. Absorption coefficients, presented as averages over slitwidth and total pressure, varied from 0.091 to 0.040 atm—1 cm—1 at 4.60 μ, 0.057 to 0.031 atm—1 cm—1 at 4.67 μ, and 0.065 to 0.026 atm—1 cm—1 at 4.72 μ, with higher values corresponding to lower temperatures. A pressure dependence of absorption was observed and an empirical correction assuming the logarithm of transmission proportional to the fourth root of total pressure was found to render Beer's law plots linear. Absorption coefficients were calculated by averaging over slitwidth an expression requiring a knowledge of the pressure dependence of integrated absorption. A comparison of these calculations with the observed values indicates quantitative agreement for 4.60 and 4.72 μ, and qualitative agreement for the temperature dependence of absorption at 4.67 μ.