H1 dynamic nuclear polarization (DNP) has been measured in supercritical ethylene in the pressure range 60-300 bar and in an external field of 1.4 T. A single-cell sapphire tube was used as a high pressure cell and powdered 1,3-bisdiphenylene-2-phenyl allyl(BDPA) free radicals were added and distributed at the wall of the cell. At all pressures the dominant DNP effect was a positive Overhauser enhancement, caused by proton-electron contact interactions at the fluid/solid radical interface. The observed enhancements varied from 12 at 67 bar to 17 at 300 bar. Besides the Overhauser enhancement, also a small solid state and thermal mixing enhancement were observed, indicating that part of the ethylene is absorbed at the radical surface for a prolonged time. These data indicate that DNP-enhanced NMR has the potential of extending the impact of NMR in research areas involving supercritical fluids.
Revised: January 14, 2003 |
Published: March 1, 2000
Citation
Wind R.A., B. Shi, J. Hu, M.S. Solum, P.D. Ellis, D.M. Grant, and R.J. Pugmire, et al. 2000.H-1 Dynamic Nuclear Polarization in Supercritical Ethylene at 1.4 T.Journal of Magnetic Resonance 143, no. 1:233-239.PNNL-SA-32121.