A new mechanism for electron spin echo envelope modulation

摘要

Electron spin echo envelope modulation(ESEEM)has been observed for the first time from a coupled heterospin pair of electron and nucleus in liquid solution.Previously,modulation effects in spin-echo experiments have only been described in liquid solutions for a coupled pair of homonuclear spins in nuclear magnetic resonance or a pair of resonant electron spins in electron paramagnetic resonance.We observe low-frequency ESEEM(26 and 52 kHz)due to a new mechanism present for any electron spin with S>1/2 that is hyperfine coupled to a nuclear spin.In our case these are electron spin(S=3/2)and nuclear spin(/= 1)in the endohedral fullerene N@C_(60)-The modulation is shown to arise from second-order effects in the isotropic hyperfine coupling of an electron and ~(14)N nucleus.