Proton-proton homonuclear dipolar decoupling in solid-state NMR using rotor-synchronized z-rotation pulse sequences

We present a theoretical analysis of rotor-synchronized homonuclear dipolar decoupling schemes that cause a z-rotation of the spins. These pulse sequences applicable at high spinning rates (nu(r)>= 30 kHz) yield high-resolution proton NMR spectra that are free of artifacts, such as zero lines and image peaks. We show that the scaled isotropic chemical-shift positions of proton lines can be calculated from the zero-order average Hamiltonian and that the scaling factor does not depend on offset. The effects of different adjustable parameters (rf field, spinning rate, pulse shape, offset) on the decoupling performance are analyzed by numerical simulations of proton spectra and by H-1 solid-state NMR experiments on NaH2PO4 and glycine.