Probing Aerogels by Multiple Quantum Filtered 131Xe NMR Spectroscopy

At the interface between solid surfaces and cavities filled with gaseous or liq. Xe, the nuclear magnetization of 131Xe (S = 3/2) is subject to quadrupolar interactions which may lead to higher rank single-quantum coherences that can be described by tensor elements T2,+-1 and T3,+-1. This can be demonstrated by multiple-quantum filtered (MQF) NMR expts. In gaseous Xe on Pyrex surfaces, the primary source of such coherences is coherent evolution induced by a nonvanishing av. quadrupolar coupling. In this contribution, MQF NMR is applied to aerogels filled with liq. Xe to demonstrate the potential of this technique for material sciences. Xe in the liq. phase provides a sufficient spin d. to obtain reasonable signal-to-noise ratios. Coherent evolution and relaxation both contribute to the creation of higher rank coherences depending on the presence or absence of H2O mols. on the surface. These 2 processes can be distinguished exptl. and provide complementary information about the surface of the host material. [on SciFinder (R)]