Emissivity of Carbon Dioxide at 43 μ

The emissivity of carbon dioxide has been measured for temperatures from 1500° to 3000°K over the wavelength range from 4.40 to 5.30 μ. Optical densities varied from 0.04 to 4.00 atm · cm; all measurements were made at a total gas pressure of 1 atm. The test gas was heated to the desired temperature by shock compression. The temperature and pressure of the test gas were determined by measuring initial concentrations and shock wave velocities. The emissivity of the hot gas was obtained in two ways: (1) the spectral radiance from the CO2 was compared to that from a globar, which was calibrated with a blackbody source and (2) the transmission through the hot gas was measured, and emissivity obtained from Kirchhoff’s law. The emissivity obtained with these two methods is in agreement within experimental error. The observed emissivities are reasonably well represented by values calculated with the weak line approximation, except that the measured values are consistently higher than the calculated emissivities at the longer wavelengths.