Generating unexpected spin echoes in dipolar solids with pi pulses.

Intrinsic origin of spin echoes in dipolar solids generated by strong ! pulses

In spectroscopy, it is conventional to treat pulses much stronger than the linewidth as delta functions. In NMR, this assumption leads to the prediction that ! pulses do not refocus the dipolar coupling. However, NMR spin echo measurements in dipolar solids defy these conventional expectations when more than one ! pulse is used. Observed effects include a long tail in the CPMG echo train for sh...

Decay of Multiple Spin Echoes in Dipolar Solids

Nuclear magnetic resonance polarization and coherence echoes in static and rotating solids

The mechanisms of defocusing and refocusing of spin order in extended dipolar coupled nuclear spin systems are investigated by experiments on static and on rotating solids. It is demonstrated that polarization or coherence echoes are possible also under magic-angle sample spinning. The dipolar interactions, averaged by the spinning, are recovered by rotor-synchronized multiple-pulse sequences. ...

Dipolar Recoupling and Decoupling

In solid state nuclear magnetic resonance spectroscopy, the magic angle spinning technique is often used to remove anisotropic interactions and generate high resolution spectra. However, these interactions contain valuable information about molecular structure and dynamics. In particular, the dipole-dipole coupling strength between two spin-1/2 nuclei is a direct reflection of their interatomic...

Multiple echoes due to distant dipolar fields in NMR of hyperpolarized noble gas solutions

We report on multiple echo measurements in hyperpolarized liquids using optically pumped spin-1/2 noble gas atoms: either Xe dissolved in cyclohexane or He dissolved in superfluid He. An NMR pulse sequence 90◦ − τ − 90◦ (with slice-selective flipping pulses for Xe experiments) was used and long echo trains have been observed in the presence of applied gradients due to average dipolar fields typ...