SPIN-LOCKING SPECTRAL LINESHAPES OF THE CENTRAL TRANSITION OF HALF-INTEGER QUADRUPOLE SYSTEMS UNDER MAGIC-ANGLE-SPINNING

The spin-locking spectra of the central transition of half-integer quadrupole systems under magic-angle spinning (SLMAS) can be exactly calculated. The lineshape patterns are much more diverse than predicted by the previous theoretical analysis based on energy level diagrams and empirical functions. The lineshapes were investigated for various values of the parameter alpha introduced by A.J. Vega (J. Magn. Reson., 96 (1992) 50) but the lineshapes cannot be completely characterized by alpha. Relaxation during spin-locking (T-1 rho) was found to be important in determining the lineshape change for different experimental parameters. An SLMAS spectrum is generally zero-order phase distortive unless the spin-locking time is the multiple of rotor spinning period. Dispersive lineshapes were demonstrated under certain conditions. The relationship between SLMAS and CPMAS is also discussed. Both theoretical and experimental results are provided.