Exclusive Formation of C^(16)O in the Prompt Oxidation of Carbon Films by ^(18)O_2 on Sm_2^(16)O_3. Implications for the Mechanism of Oxygen Activation

The oxidation of carbon films on Sm_2^(16)O_(3-γ) exposed to ∼1 Langmuir/s ^(18)O_2 at 1100 K solely yields C^(16)O while the substrate is quantitatively capturing oxygen. This is evidence that chemisorbed ^(18)O scrambles its label with the catalyst before oxidizing carbon or diffusing into the bulk oxide. O-diffusion coefficients measured in samaria under present conditions (D_O ≥ 8 × 10^(-9) cm^2 s^(-1) above 1000 K) imply that scrambling is complete in a few nanoseconds. We infer that dissociative ^(18)O_2 chemisorption is assisted by the concomitant restructuring of extended surface regions, on which carbon films are oxidized by the statistically preponderant unlabeled oxygen species.