The infra-red spectra of the surface complexes which are produced when O3, O2, NO, N2O and H2O2 react with very thin hydrogen-free carbon films have been determined and discussed in terms of previously published kinetic studies. The major peaks are: (i) the 5.7 µ peak, attributed to carbonyl groups, (ii) the 6.4 µ peak, attributed to lactone groups, and (iii) the 7.4 µ peak, attributed to hydroxyl groups when it appears with H2O and H2O2, or to carbonyl groups when it accompanies the strong 5.7 µ peak.