Note on Absorption Coefficients of Hot CO2 at 4.40 μ

Abstract

The infrared absorption of CO₂–N₂ mixtures, enclosed in a furnace‐heated gas cell, was studied for optical depths of 0.10 to 2.5 cm‐atm at 1273°K. The results of these measurements were compared to results for shock‐heated CO₂–N₂ mixtures, obtained for the range 0.10 to 0.40 cm‐atm. The results did not appear to depend upon the method of heating, whether furnace or shock tube. However, the results did depend strongly upon pressure. Two types of Beer's law failure were found: (1) When the ratio of CO₂ pressure to total pressure was kept constant, plots of reciprocal transmittance vs optical depth were straight lines through the origin, of slope (absorption coefficient) dependent on the pressure ratio; (2) similar plots for constant total pressure were concave toward the optical depth axis. These effects are due to varying pressure broadening of unresolved spectral lines.