Comparing radical diffusion crossover phenomena in alkanes and alcohols

We applied electron spin resonance (ESR) to study tracer diffusivities of a nitroxide radical at various temper-atures in the normal alkanes (octane to tridecane) and alcohols (methanol to 1-octanol). We studied and compared radical diffusivities in these liquids because their molecules are similar, but alcohols exhibit hetero-geneous structures due to the hydrogen bonding of hydroxyl groups, which is absent in alkanes. The crossover temperature behavior of radical diffusivities was found in all liquids by relating radical diffusivities and solvent self-diffusivities. This finding evidences the transformation from a single-molecule diffusion process into a col-lective process upon temperature lowering. However, the crossover behavior strongly differs in alcohols and alkanes, indicating that the heterogeneous structure of alcohols affects the radical diffusion crossover.