Magic-Angle Spinning Nuclear Magnetic Resonance of Half-Integer Quadrupole Nuclei: Effect of Spin-Locking Efficiency on Powder Lineshapes

S. Hayashi
[Solid State Nuclear Magnetic Resonance, Vol.3, pp.93-101, 1994]

²³Na spin-lock magic-angle spinning (MAS) and cross-polarization (CP) MAS nuclear magnetic resonance (NMR) spectra have been traced for sodium-containing compounds such as Na₂SnO₃ · 3H₂O, Na₂TeO₄ · 2H₂O, Na₂SiO₃ · 9H₂O and NaBO₂ · 2H₂O whose asymmetric factors in quadrupole interaction are 0.00, 0.37, 0.63 and 0.80, respectively. The lineshapes in the spin-lock/MAS and CP/MAS NMR spectra are different from those in the spectra measured with the single-pulse sequence (SP) combined with ¹H dipolar decoupling (DD). In other words, the former lineshapes are distorted from the theoretical ones broadened by the second-order quadrupole interaction. The lineshapes are distorted during the spin-locking period, since the spin-locking efficiency depends on the crystallite orientation in a powder sample. We have discussed the distortion on theoretical bases and simulated the observed spectra as shown in Fig.1.