31P NMR chemical shielding tensors of α-Ca2P2O7

Abstract

The ³¹P NMR chemical shielding tensors were measured in a crystal of α‐Ca₂P₂O₇; the principal values, relative to 85% H₃PO₄, were found to be −42, 32, 65 ppm for P(1) and −48, 44, 67 ppm for P(2) with an average relative standard deviation of 7%. The most probable orientations of the tensors in the molecule were determined, and in both cases the most downfield component of the shielding tensor is along the P–O(P) bond direction; this orientation is correlated with the electronic distribution around the phosphorous nuclei. The high resolution spectra used in determing the shielding tensors were taken using the multiple pulse WAHUHA technique which removes homonuclear dipolar interactions in solids [J. S. Waugh, L. M. Huber, and U. Haeberlin, Phys. Rev. Lett. 20, 180 (1968)]. The linewidths were reduced from 1 KHz to 100 Hz by this technique. Details of the spectrometer design and the tuneup procedure for the WAHUHA experiment are also given.