Complexes formed by low dose irradiation with electron (1015-16/cm2) and He (5x1012- 5x1013/cm2) in the relatively low carbon concentration (1016/cm3) MCZ silicon were investigated by highly sensitive and quantitative IR absorption analysis. CiOi and VO were the main complexes in all cases. The concentration of these complexes was about 1015/cm3, or 10% of included carbon in the highest case. Loss of almost equal amount of Cs was observed. The concentration of CiOiI was one order of magnitude lower. Upon annealing, these lines weakened and almost disappeared at 400 oC. There were some absorption lines introduced by the annealing. VO2 was strongest among them and CsOi related structure was also confirmed. There were absorption lines at 954.9 and 962.6 cm-1 appeared after annealing at 300 oC.