Double-quantum cross-polarization NMR in solids
Double-quantum NMR is a useful way to obtain spectra of quadrupolar nuclei (/sup 2/D, /sup 14/N, ...) in solids. This allows measurements of the chemical shifts for these nuclear spins. The theory of Hartmann-Hahn cross polarization between I=1/2 and such S=1 spins is discussed. Particular attention is drawn to the cross polarization of the double-quantum transition. The thermodynamics and the dynamics of the process are evoked in detail using a fictitious spin-1/2 formalism. The spin S=1 Hamiltonian can always be factored into two commuting parts (independent thermodynamic reservoirs), one of which behaves as a fictitious spin 1/2 which is cross polarized with the I=1/2 spins. Modified Hartmann-Hahn conditions emerge from the theory, and the dependence of cross-polarization times T/sub I/S on rf intensity and frequency for spin locking and adiabatic demagnetization in the rotating-frame experiments are calculated. Measurements on the /sup 1/H-/sup 2/D double resonance in dilute solid benzene-d/sub 1/ are reported, verifying the predictions and indicating that cross polarization provides a sensitive means of detecting the /sup 2/D double-quantum transition. Values are reported for the thermodynamic parameters and cross-polarization times as a consequence. Three possible versions of double-resonance detection of double-quantum spectra are possible: direct detection of the cross-polarized double-quantum decay, indirect detection of the frequency spectrum following Hartmann and Hahn, and indirect detection of the free-induction decay following Mansfield and Grannell.
- Research Organization:
- Department of Chemistry and Materials and Molecular Research Division, Lawrence Berkeley Laboratory, University of California, Berkeley, California 94720
- OSTI ID:
- 5237104
- Journal Information:
- Phys. Rev., A; (United States), Vol. 22:2
- Country of Publication:
- United States
- Language:
- English
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