Negative cross-peaks have been observed in the (19)F 2-D magnetization-exchange MAS NMR spectra of Ba(2)MoO(3)F(4) under fast-spinning conditions. The polarization transfer dynamics are studied as a function of the spinning frequency and the frequency separation of the resonances. The results are consistent with a novel mechanism, in which four spins simultaneously exchange Zeeman magnetization with each other, in an energy-conserving process.
Copyright 1999 Academic Press.