Infrared absorption measurements were made of the localized vibrational modes due to defects produced in Czochralski-grown Si material after irradiation with fast neutrons and subsequent thermal treatments. The investigation was focused, in particular, on three satellite bands in the region of the A center, located at 839, 833 and 824 cm−1respectively, the annealing behavior of which was carefully monitored. Correlation of our results with previous infrared, electron paramagnetic resonance and positron annihilation studies favors attributing these bands to theV2O,V3O2and V2O2defects respectively. In addition, semiempirical calculations were carried out for the vibrational frequencies of these defects, and the predicted values are in agreement with the above assignments. ©1997 American Institute of Physics.