Spin-locking mechanism of spin I=3/2 quadrupolar nuclei undergo magic angle spinning

The spin-locking mechanism of the spin I = 3/2 quadrupolar nuclei under mag ic angle spinning (MAS) has been theoretically and experimentally investiga ted, and the criterion of adiabatic passage around zero-crossings of the qu adrupole splitting was inferred from the time-dependent Shrodinger equation in this article. The theory, numerical simulations, and experiments conduc ted in this work all indicated that second-order quadrupole interaction and off-resonance play important roles in the spin-locking of the quadrupolar nuclei, and they were responsible for the great loss of the spin-locking si gnals. The spin-locking for a spin I = 3/2 nucleus might be achieved by min imizing the effect of the second-order quadrupole interaction by using a ra dio frequency (RF) offset. This offset was realized by setting the RF to th e opposite position of the isotropic second-order quadrupolar shift of sing le quantum coherences. (C) 2000 Elsevier Science B.V. All rights reserved.