Tracking the Ultrafast Dynamics of Carbon–Carbon Bond Formation Following CH 3 I Photodissociation on Amorphous Silicon Oxide Surfaces

Carbon–carbon (C─C) bond formation at solid interfaces is central to heterogeneous catalysis and surface photochemistry, yet the ultrafast dynamics of radical coupling at surfaces remain poorly resolved. Here, we investigate the time‐resolved formation of C─C bonds following the photodissociation of CH 3 I adsorbed on an amorphous silicon oxide surface. Femtosecond pump–probe spectroscopy combined with time‐of‐flight mass spectrometry is used to track the transient evolution of intermediates and reaction products with temporal, mass, and energy resolution. The CH 3 I photoexcitation at 266 nm induces rapid C─I bond cleavage, generating CH 3 and I fragments whose evolution reveals distinct energy dissipation and reaction pathways. The methyl radicals undergo rapid translational energy loss within the first few picoseconds, enabling bimolecular interactions at the surface. Time‐resolved detection of C2 fragments (C 2 H 4 + and C 2 H 5 + ), produced via probe‐induced dissociative ionization of ethane, provides direct signatures of methyl radical coupling. The earliest appearance of these products at ~0.4 ps establishes a lower bound for surface‐mediated C─C bond formation, while their subsequent growth reflects the interplay between thermalization, diffusion, and encounter probability. These findings provide femtosecond‐resolved insight into radical coupling on structurally disordered oxide surfaces and extend ultrafast surface reaction studies beyond crystalline model systems.