Multiple quantum coherence in HYSCORE spectra

The implementation of matched pulses in two-dimensional electron spin echo envelope modulation experiments results in a drastic increase in intensity of peaks representing nuclear multiple quantum coherence. For a spin system consisting of one electron spin S = 1/2 and two nuclei with spin I = 1/2 t he nuclear coherence created by the sequence (pi /2)-tau-(pi /2) is calcula ted. The transfer amplitudes between different kinds of nuclear coherences of a microwave pi pulse are given. A new matched HYSCORE pulse sequence, ca lled SMART HYSCORE, is introduced with only one microwave pulse for the gen eration and detection of nuclear coherence, which does not suffer from blin d spots. This sequence is applied to a single crystal and a disordered syst em, and it is demonstrated how the resolution of weakly coupled nuclei can be increased. Furthermore we show that information about the relative sign of hyperfine couplings and about the relative orientation of the hyperfine tensors can be derived from the ridge patterns in a HYSCORE experiment. The numerical simulations are confirmed experimentally. (C) 2001 American Inst itute of Physics.