The conversion of semiconductive SrCuO2‘‘infinite layer’’ epitaxial films into a metallic and superconducting (Tc&bartil;30 K) oxycarbonate phase related to Sr2CuO2(CO3) has been induced by thermal processing in oxidizing ambient containing a small amount of CO2. Ion beam analysis using the resonant12C(p,p)12C elastic backscattering cross section for protons incident at 1.73 MeV confirms the presence of substitutional C in the converted perovskite lattice. Comparison of the threshold CO2partial pressure with thermodynamic stability data for SrCO3suggests that the conversion is initiated by the high affinity of Sr(O) for CO2. ©1995 American Institute of Physics.