Creating isotropic dipolar spectra for a pair of dipole coupled spins in high-field

In the absence of a strong magnetic field, the dipolar interaction between two nuclear spins is independent of orientation leading to sharp lines. However, in high magnetic fields the Zeeman interaction breaks the symmetry of space and spin producing an anisotropic dipolar spectra. In the following Letter, a method that yields isotropic dipolar spectra for a pair of dipole-coupled spins is presented. This is accomplished through a suitable choice of coherence pathways and average Hamiltonians. We present a theoretical explanation as well as an experimental verification for this novel methodology.