Zero Field NMR Entirely in High Field: Theoretical Background and Experimental Proposals.

The theoretical basis is presented for a new class of multiple pulse nuclear magnetic resonance (NMR) experiments. The experiments are designed to transform the broad, "powder pattern" lineshapes that are commonly observed in spectra of solids with strong dipole-dipole couplings between nuclei into sharp lines with splittings that depend only on internuclear distances. It is shown that this transformation can be brought about by the combination of rapid sample rotation with the synchronous application of the proper sequence of radio frequency pulses. An average Hamiltonian theory analysis of such experiments is given, and a specific pulse sequence is proposed. The proposed experiments effectively remove the orientation dependence from spin-spin couplings, giving the NMR spectra a "zero field" appearance even though the experiments are carried out entirely in high field. Since the resulting spectra depend only on internuclear distances, these methods promise to have important applications in studies of molecular conformations and in studies of radial distribution functions of impurities and dopants in solids.