High-resolution H-1 NMR spectroscopy of absorbed molecules in the presenceof strong magnetic fields

H-1 NMR spectra of molecules sorbed in porous materials may be strongly inf luenced by the presence of local magnetic fields due to susceptibility broa dening which is a result of the polarization of the adsorbent grains in par ticular in strong magnetic fields. The linewidth can be essentially reduced by the application of magic angle spinning (MAS) techniques but is also de termined by the translational motion of the adsorbed species over mean dist ances which are comparable to the dimensions of the grains. The lineshape a nalysis was performed on the basis of a modified Anderson-Weiss theory as p roposed by Fenzke et al. and compared with H-1 NMR spectra measured for but ene molecules sorbed in NaX-type zeolites at various external fields B (up to 17.6.T) and different MAS frequencies. A considerable gain in resolution of the chemical shifts by using high magnetic fields is established. Copyr ight (C) 2000 John Wiley & Sons, Ltd.