Artifacts in Experimental and Simulated Solid-State ²H NMR Powder Spectra

Two types of artifacts in solid-state ²H NMR echo spectra that may be confused with spectral changes resulting from molecular motion of a deuterated phenyl ring undergoing π flips are investigated. The first type of artifact arises from improperly determining the initial point of the FID (i.e., the echo maximum). If sampling begins after the top of the echo, the spectrum has the appearance of resulting from a log-Gaussian distribution of correlation times (i.e., flip rates). A specifically deuterated sample of 1,4-bis(1,3-octadecadiynyl)benzene is used to illustrate this effect. The second type of artifact results from computational limitations in the simulation of ²H NMR echo spectra. To accommodate corrections necessary to mimic experimental conditions in simulated spectra, it is easier to work in the time domain. Recursion has been suggested as a means for efficiently propagating the simulated FID. However, finite computer precision results in the "blurring" of the long-time components of the FID and thus the subsequent omission of fine spectral structure from the simulated spectra. An alternative method is suggested in which the FID is propagated using recursive cycles. This method retains much of the efficiency of the recursive method while retaining the fine spectral structure.