Electron Spin Relaxation Rates T_1~(-1) and T_2~(-1) in Diluted Solid N@C_(60)

摘要

We report on pulsed electron-spin-resonance (ESR) investigations of endo-hedral N@C_(60)-The measurements were performed in X band (9.5 GHz) and W band (94 GHz). Applying a two-pulse sequence with a variable flip angle of the second pulse, we could not only separate the contributions of the central and the satellite transitions, but also monitor the phase transition in C_(60) at T≈250 K. Analysing the temperature dependence of the longitudinal relaxation rate T_1~(-1), the hyperfine relaxation, which is caused by the damped quantum oscillator of the nitrogen atom inside C_(60), was found to play the most important role. Prom a comparison of the experimental data with our relaxation model, the oscillator energy was determined to be E_(osc)≈11(2) meV.