EFFICIENT TIME PROPAGATION TECHNIQUE FOR MAS NMR SIMULATION - APPLICATION TO QUADRUPOLAR NUCLEI

The quantum mechanical Floquet theory is investigated in order to deri ve an efficient way of performing numerical calculations of the dynami cs of nuclear spin systems in MAS NMR experiments. Here, we take advan tage of time domain integration of the quantum evolution over one peri od as proposed by Eden et al. (1). But a full investigation of the pro pagator U(t, t(0)), and especially its dependence with respect to t an d t(0) within a formalized approach, leads to further simplifications and to a substantial reduction in computation time when performing pow der averaging for any complex sequence. Such an approximation is suita ble for quadrupolar nuclei (I > 1/2) and can be applied to the simulat ion of the RIACT (rotational induced adiabatic coherence transfer) phe nomenon that occurs under special experimental conditions in spin lock ing experiments (2-4). The present method is also compared to the usua l infinite dimensional Floquet space approach (5, 6), which is shown t o be rather inefficient. As far as we know, it has never been reported for quadrupolar nuclei with I greater than or equal to 3/2 in spin lo cking experiments. The method can also be easily extended to other are as of spectroscope. (C) 1998 Academic Press.