NMR with a continuously circulating flow of laser-polarized Xe-129

In this paper we describe the construction of an apparatus for optical pump ing of Xe-129 in a circulating gas system connected to a probe for static h igh-field NMR. The optimal working conditions for the optical pumping under flow are explored, yielding a continuous gas now with a steady-state spin- polarization of about 2%. It is shown that on various types of high surface area materials a steady-state of adsorbed laser-polarized xenon can be;rea ched with polarizations of about 0.3%. NMR spectroscopy of this layer is gr eatly facilitated due to the renewable magnetization under the continuous-f low conditions allowing unprecedented fast detection of two-dimensional NMR experiments with laser-polarized Xe. The steady-state spin-polarization of adsorbed Xe-129 gives rise to cross-relaxation to surface nuclei such as H -1 and Si-29. A direct spin-polarization-induced nuclear Overhauser effect (SPINOE) to heteronuclei is observed with an enhancement factor of about 20 -30. A method is presented for simple modulation of the spin-polarization d irection in the fringe field of the high-field magnet; this is exploited to obtain difference SPINOE spectra to highlight only the surface nuclei. Fur thermore, a transfer via cross-polarization (CP) from adsorbed Xe to surfac e protons is demonstrated to select surface groups with reduced mobility co mpared to SPINOE detection.