A bimodal Floquet analysis of phase modulated Lee-Goldburg high resolution proton magic angle spinning NMR experiments

A description of phase modulated Lee-Goldburg experiments PMLG-n, with 2n pulses per rf cycle, on coupled proton systems under magic angle spinning is presented using bimodal Floquet theory. Level crossing conditions between Floquet states are derived and perturbation theory is used to account for spectral changes as a function of the spinning frequency and the number of pulses per PMLG-n sequence. High resolution solid-state proton spectra are shown that are obtained for n equal to 9, 5 and 3. Line broadening and the rf rotor frequency line positions are correlated to level anticrossings. (C) 2000 Elsevier Science B.V.