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An electric arc-driven shock tube was used to study the effect of composition on the radiation from shock-heated mixtures of 9% CO 2 -90% N 2 -l% A, 30% CO 2 -70% N 2 , and 100% CO 2 . Measurements were made of the shock-layer radiance at the stagnation point of a flat-faced cylinder in the 0.3-to 2.7-ju. region, using a carbon-coated thin film gage for flight velocities from 20,000 to 46,000 fps and initial pressures varying from 0.25 to 2.00 mm Hg. Shock standoff distances were measured by photographic techniques. Photometric measurements were made of the intensity behind the incident shock in the 0.3-to 1.0-/i region, and a tungsten photoelectric gage measured the nonequilibrium intensity in the far ultraviolet region. Shock front integrated nonequilibrium and equilibrium intensities, nonequilibrium relaxation distances, and time to peak intensity were obtained. Stagnation-point radiance results are higher than one current estimate at high temperatures and low densities. Integrated nonequilibrium intensity for 9% CO 2 -90% N 2 -l% A mixtures was 32 w/cm 2 -27T sr at 25,000 fps. Major radiating species are identified as the CN radical for CO 2 -N 2 mixtures and the CO + ion for 100% CO 2 . Oscillator strengths for the CN red and violet systems are deduced from the measurements. The/ value results indirectly give support to a dissociation energy of 7.7 ± 0.1 ev for the CN radical.