Triple quantum cross-polarization NMR of ~1H/~(27)Al and ~(19)F/~(23)Na spin systems in solids

摘要

Changes in the triple quantum cross-polarization (TQCP) matching profiles and ~(27)Al/~(23)Na second-order quadrupolar lineshapes, are observed as a function of the I = 1/2 rf field strength for both static and MAS conditions. These were interpreted by considering the orientation dependence of the nutation frequency associated with the TQ transition. Only a fraction of the spins in the powder, with specific orientations of the EFG tensor, can match the Hartmann-Hahn condition at the same time, for a fixed I = 1/2 rf field strength. Good fits between ~(19)F -> ~(23)Na experimental and calculated TQCP lineshapes were observed for moderate to high ~(19)F rf field strengths.