Strong coupling quantum chemical equations

There are several ways to enhance spin diffusion in such systems. One can broaden the zero-quantum line to such an extent that the intensity at frequency zero is non vanishing for all relevant chemical-shift differences. However, due to the normalization of the zero-quantum line, a broad line implies that the intensity/,y(0) is low and that the spin diffusion proceeds slowly. A broadening of the zero-quantum line can often naturally be achieved by the coupling to a strongly-coupled proton spin system in so-called proton-driven spin diffusion while the form of the heteronuclear dipolar-coupling Hamiltonian (Equation (4.3)) prevents polarization exchange with the protons, the... 

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