A Simple Technique for Determining Nuclear Quadrupole Coupling Constants with RAPT Solid-State NMR Spectroscopy

An enhanced Rotor Assisted Population Transfer (RAPT) experiment is presented and used as a simple and fast technique to measure the magnitude of the nuclear quadrupolar coupling constant of half-integer quadrupolar nuclei. The enhanced RAPT sequence consists of a train of Gaussian pulses with alternating off-resonant frequencies of +/-nuoff. Simulated and experimental results demonstrating the method are given in the case of 87Rb (spin 3/2) and 27Al (spin 5/2) nuclei. The RAPT sequence is also used to selectively suppress resonances based on their quadrupolar coupling constant.