Surface diffusion of the cyclohexadienyl radical adsorbed on silica and on a silica supported Pd catalyst studied by means of ALC-μSR Original Research Article

The dynamic behaviour of the cyclohexadienyl radical adsorbed on plain silica and on a silica supported Pd catalyst is investigated by means of the avoided-level-crossing muon spin resonance technique. The influence of benzene coverage and of surface texture on the hyperfine coupling constants, on the signal amplitudes and on the mobility of the radical is studied. Information about surface diffusion is obtained using a theoretical model based on a stochastic Liouville formalism. The radical mobility increases with coverage of the surface with benzene. Arrhenius parameters are discussed within the framework of a hopping model based on transition-state theory for surface diffusion. It is suggested that the dynamics of the surface hydroxyl groups play a crucial role in the diffusion process.