Right-angle spinning for sensitivity improvement in pulse EPR experiments

Right-angle spinning EPR, in which the sample is rotated about an axis perpendicular to the static magnetic field, is introduced for improvement of the sensitivity of pulse EPR experiments on orientationally disordered systems. Often the range of excitation of the microwave pulses is much narrower than the spectral width, so that only a small fraction of the spins is involved in the experiment. Under right-angle spinning these spins are shifted off-resonance and spins still in thermal equilibrium become resonant, resulting in an increase in repetition rate and thus in sensitivity. The principles of the new approach are described, and experiments are presented in which the measuring time is found to be reduced by a factor of more than 200.