Infrared absorption measurements were made before and after low‐temperature electron irradiations of silicon samples which contained either dispersed oxygen, carbon, or carbon plus oxygen. Two distinctly different centers are formed upon low‐temperature irradiation depending upon the carbon and oxygen content. One center is the well‐known vacancy‐oxygenA‐center defect (836 cm−1) and is formed in oxygen‐containing silicon with a magnitude which is independent of the carbon content. The other center (922 and 932 cm−1) is formed only in silicon crystals which containbothoxygen and carbon. The results indicate that this center is formed by the trapping of a silicon interstitial at a carbon‐oxygen complex.