SYNCHRONOUS ACCUMULATION OF POLARIZATION - A NEW APPROACH TO CROSS-POLARIZATION UNDER FAST MAGIC-ANGLE-SPINNING

A new experiment to circumvent the problem of poor cross polarisation (CP) efficiency at the Hartmann-Hahn match under high-speed magic angle spinning is proposed and tested in the case of adamantane. It is based on the fact that the polarisation transferred from the I spin to the S spin, though zero for a full rotor cycle, is finite for a part of a cycle. The polarisation acquired during a part of every rotor cycle is accumulated for several cycles to be finally observed as the signal. This is achieved by a simple modification to the regular CP experiment and has been shown to give rise to enhanced efficiency at the standard CP condition.