Relative CSA-dipolar orientation from REDOR sidebands

Algebraic expressions are given for the sideband intensities of REDOR dephasing experiments as a function of the relative orientation of the CSA and dipolar tensors. The expressions are straight-forward to derive and implement and can be easily modified for variations in the spin systems, including distributions of distances and multiple dephasers. These expressions, along with the high sensitivity, resolution, and general robust nature of REDOR, make determining CSA-Bipolar orientations from REDOR experiments reliable and, compared to full simulations, efficient and routine. Additionally, it is shown that even the +/-1 sidebands of fast-spinning samples may contain significant information about orientation. Finally, numerical integration of the expressions supports the intuitive notion that any difference in the sideband dephasing rates is evidence of preferred CSA-Bipolar orientations. This fact can be used to gauge the extent of local molecular order in intermolecular dephasing experiments. (C) 2002 Elsevier Science.