Cross polarization in electron nuclear double resonance by satisfying the Hartmann-Hahn condition

The polarization of electronic spins S is transferred to nuclear spins / by cross relaxation in an electron nuclear double resonance experim ent. The cross relaxation becomes very efficient with a time constant Tcr o about 0.5 m icroseconds if the Hartmann-Hahn condition is satisfied for electronic spins S spin-locked to the microwave field B1,s in the rotating frame and for proton spins / in the static magnetic field B0