Electron Spin Resonance and Relaxation Studies of Internal Motion in CH2CO2− Radicals Trapped in γ-Irradiated Sodium Acetate Crystals

CH₂CO₂⁻ radicals are stable in γ‐irradiated sodium acetate crystals. The ESR spectra of CH₂CO₂⁻ and carbon‐13 labeled radicals, CH₂¹³CO₂⁻ and ¹³CH₂CO₂⁻, were studied in detail in the temperature range of 77°K to room temperature. It was found that the CH₂ group executes an internal motion which is characterized by proton exchange in the oriented radicals. The motion is slowed on lowering the temperature, giving rise to an electron spin relaxation time of the order of microseconds at 77°K. The correlation time for the motion was found to be temperature dependent, varying as exp $\mathrm{(V\hspace{0.17em}/\hspace{0.17em}kT)}$ with an activation energy $V$ of the order of 3 kcal mole⁻¹.