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Title: {sup 19}F/{sup 23}Na multiple quantum cross polarization NMR in solids

Abstract

{sup 19}F{yields}{sup 23}Na triple quantum (TQ) cross polarization (TQCP) experiments and numerical simulations have been performed on the oxyfluoride NaMoO{sub 3}F. Due to the orientation dependence of the quadrupolar tensor and thus the TQ nutation frequency ({omega}{sub s,nut}), only a fraction of the spins in the powder can match the Hartmann-Hahn condition at the same time, for a fixed {sup 19}F rf field strength ({omega}{sub 1I}). Numerical simulations of the static TQCP process, for different single crystallite orientations, demonstrate that the most efficient TQCP occurs for parts of the powder where the quadrupolar splitting, Q{sup '}, is largest, and where the TQ coherences are pure eigenstates of the system, even though {omega}{sub s,nut} is smallest for these orientations. Under magic angle spinning (MAS) conditions, {omega}{sub s,nut} becomes time dependent and again, efficient TQCP is observed at times during the rotor period where Q{sup '} is largest. TQCP intensities for different crystallites were calculated as a function of {omega}{sub 1I}, for fixed {sup 23}Na rf field strengths, to obtain TQCP matching profiles and to determine optimum Hartmann-Hahn conditions. The TQCP matching profiles vary significantly with crystallite orientation and with spinning speed, due to the different time dependences of the quadrupolar interactionmore » for the different orientations. Centerband matching conditions are observed at {sup 19}F rf fields, close to the minimum values of {omega}{sub s,nut} observed during the rotor period. Two different centerbands are observed for crystallite orientations where there are two different local minima for {omega}{sub s,nut}. The time dependence of {omega}{sub s,nut} results in higher-order (>2) sideband matching conditions. The experimentally observed static and MAS TQCP NMR matching profiles, and changes in the {sup 23}Na static and MAS second-order quadrupolar NMR lineshapes, could be rationalized on the basis of the calculated distributions of {omega}{sub S,nut} that occur within the powder. Optimum TQCP intensities were obtained with high {sup 23}Na rf power, to maximize {omega}{sub s,nut}, and slow MAS, to ensure efficient spin-locking; a further increase in intensity could be achieved by ramping the {sup 19}F rf field during the contact time. The efficiencies of the single quantum cross polarization (SQCP) multiple quantum (MQ) MAS and TQCP-MQMAS experiments were compared and were found to be very similar for NaMoO{sub 3}F. Finally, the two-dimensional TQCP-MQMAS experiment was illustrated. (c) 2000 American Institute of Physics.« less

Authors:
 [1];  [1]
  1. Department of Chemistry, State University of New York at Stony Brook, Stony Brook, New York 11794-3400 (United States)
Publication Date:
OSTI Identifier:
20216009
Resource Type:
Journal Article
Journal Name:
Journal of Chemical Physics
Additional Journal Information:
Journal Volume: 112; Journal Issue: 17; Other Information: PBD: 1 May 2000; Journal ID: ISSN 0021-9606
Country of Publication:
United States
Language:
English
Subject:
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND SUPERFLUIDITY; NMR SPECTRA; FLUORINE 19; SODIUM 23; OXYFLUORIDES; SOLIDS; LINE WIDTHS; QUADRUPOLE MOMENTS; EXPERIMENTAL DATA

Citation Formats

Lim, Kwang Hun, and Grey, Clare P. {sup 19}F/{sup 23}Na multiple quantum cross polarization NMR in solids. United States: N. p., 2000. Web. doi:10.1063/1.481347.
Lim, Kwang Hun, & Grey, Clare P. {sup 19}F/{sup 23}Na multiple quantum cross polarization NMR in solids. United States. doi:10.1063/1.481347.
Lim, Kwang Hun, and Grey, Clare P. Mon . "{sup 19}F/{sup 23}Na multiple quantum cross polarization NMR in solids". United States. doi:10.1063/1.481347.
@article{osti_20216009,
title = {{sup 19}F/{sup 23}Na multiple quantum cross polarization NMR in solids},
author = {Lim, Kwang Hun and Grey, Clare P.},
abstractNote = {{sup 19}F{yields}{sup 23}Na triple quantum (TQ) cross polarization (TQCP) experiments and numerical simulations have been performed on the oxyfluoride NaMoO{sub 3}F. Due to the orientation dependence of the quadrupolar tensor and thus the TQ nutation frequency ({omega}{sub s,nut}), only a fraction of the spins in the powder can match the Hartmann-Hahn condition at the same time, for a fixed {sup 19}F rf field strength ({omega}{sub 1I}). Numerical simulations of the static TQCP process, for different single crystallite orientations, demonstrate that the most efficient TQCP occurs for parts of the powder where the quadrupolar splitting, Q{sup '}, is largest, and where the TQ coherences are pure eigenstates of the system, even though {omega}{sub s,nut} is smallest for these orientations. Under magic angle spinning (MAS) conditions, {omega}{sub s,nut} becomes time dependent and again, efficient TQCP is observed at times during the rotor period where Q{sup '} is largest. TQCP intensities for different crystallites were calculated as a function of {omega}{sub 1I}, for fixed {sup 23}Na rf field strengths, to obtain TQCP matching profiles and to determine optimum Hartmann-Hahn conditions. The TQCP matching profiles vary significantly with crystallite orientation and with spinning speed, due to the different time dependences of the quadrupolar interaction for the different orientations. Centerband matching conditions are observed at {sup 19}F rf fields, close to the minimum values of {omega}{sub s,nut} observed during the rotor period. Two different centerbands are observed for crystallite orientations where there are two different local minima for {omega}{sub s,nut}. The time dependence of {omega}{sub s,nut} results in higher-order (>2) sideband matching conditions. The experimentally observed static and MAS TQCP NMR matching profiles, and changes in the {sup 23}Na static and MAS second-order quadrupolar NMR lineshapes, could be rationalized on the basis of the calculated distributions of {omega}{sub S,nut} that occur within the powder. Optimum TQCP intensities were obtained with high {sup 23}Na rf power, to maximize {omega}{sub s,nut}, and slow MAS, to ensure efficient spin-locking; a further increase in intensity could be achieved by ramping the {sup 19}F rf field during the contact time. The efficiencies of the single quantum cross polarization (SQCP) multiple quantum (MQ) MAS and TQCP-MQMAS experiments were compared and were found to be very similar for NaMoO{sub 3}F. Finally, the two-dimensional TQCP-MQMAS experiment was illustrated. (c) 2000 American Institute of Physics.},
doi = {10.1063/1.481347},
journal = {Journal of Chemical Physics},
issn = {0021-9606},
number = 17,
volume = 112,
place = {United States},
year = {2000},
month = {5}
}