NMR with a continuously circulating flow of laser-polarized {sup 129}Xe
- Lawrence Berkeley National Lab., CA (United States). Materials Sciences Div.
In this paper the authors describe the construction of an apparatus for optical pumping of {sup 129}Xe in a circulating gas system connected to a probe for static high-field NMR. The optimal working conditions for the optical pumping under flow are explored, yielding a continuous gas flow 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 reached with polarizations of about 0.3%. NMR spectroscopy of this layer is greatly facilitated due to the renewable magnetization under the continuous-flow conditions allowing unprecedented fast detection of two-dimensional NMR experiments with laser-polarized Xe. The steady-state spin-polarization of adsorbed {sup 129}Xe gives rise to cross-relaxation to surface nuclei such as {sup 1}H and {sup 29}Si. 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 direction in the fringe field of the high-field magnet; this is exploited to obtain difference SPINOE spectra to highlight only the surface nuclei. Furthermore, a transfer via cross-polarization (CP) from adsorbed XE to surface protons is demonstrated to select surface groups with reduced mobility compared to SPINOE detection.
- Sponsoring Organization:
- USDOE, Washington, DC (United States)
- DOE Contract Number:
- AC03-76SF00098
- OSTI ID:
- 351596
- Journal Information:
- Journal of Physical Chemistry B: Materials, Surfaces, Interfaces, amp Biophysical, Vol. 103, Issue 22; Other Information: PBD: 3 Jun 1999
- Country of Publication:
- United States
- Language:
- English
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