DIFFUSION OF THE TRIMETHYL-CYCLOHEXADIENYL RADICAL ADSORBED ON SILICA- REDFIELD THEORY AND RESULTS OF MU-SR EXPERIMENTS

The 2,4,6-trimethyl cyclohexadienyl radical adsorbed on a fully hydrox ylated silica surface was investigated using the rime-differential and lime-integrated muon spin resonance techniques near avoided crossings of magnetic energy levels in high longitudinal magnetic fields. Infor mation about surface diffusion is obtained from the relaxation resulti ng from the partial averaging of the hyperfine anisotropy when the ads orbed species diffuses over the surface of a sphere. A Redfield formal ism is developed to analyse the stochastic motion in terms of diffusio n coefficients. The results agree with those of a stochastic Liouville approach reported previously. Diffusion of the trimethyl-substituted radical is described by the same Arrhenius frequency factor but a cons iderably higher activation energy than that of the unsubstituted analo gue.