Fine Structures of 1H-Coupled 13C MAS NMR Spectra for Uniaxially Rotating Molecules in Deuterated Surroundings: Conformations of n-Alkane Molecules Enclathrated in Urea Channels

Efficient spectral simulations in NMR of rotating solids. The gamma-COMPUTE algorithm

We explore the time-translational relation between one of the powder angles (gamma) and the sample rotation angle (omegart) in NMR spectroscopy of rotating solids. Averaging over the gamma powder angle is shown to be generally equivalent to a cross correlation of two periodic functions. This leads to a fundamental relation concerning the phases of NMR spectra of rotating solids as well as improved strategies for efficient simulation of experimental spectra. Using these results in combination with the frequency-domain simulation procedure COMPUTE (M. Edén et al., J. Magn. Reson. A 120, 56 (1996)), it proves possible to reduce the computation time for spectral simulations by typically a factor 10-30 relative to the state-of-the-art calculations using the original COMPUTE algorithm. The advantage and the general applicability of the new simulation procedure, referred to as gamma-COMPUTE, are demonstrated by simulation of single- and multiple-pulse MAS NMR spectra of 31P-31P and 1H-1H spin pairs influenced by anisotropic chemical shielding and homonuclear dipolar interactions.