Real figure of two-dimensional spin-echo NMR spectra for a homonuclear two-spin system in rotating solids

Abstract

Two-dimensional (2D) spin-echo NMR experiments have been carried out on polycrystalline [2,3-13C2]-alanine under magic-angle sample spinning (MAS) conditions, so that two unusual resonance lines emerged along the F1 axis (Kuwahara, D., Nakai, T., Ashida, J., and Miyajima, S., 1999, Chem. Phys. Lett., 305, 35). To examine the spectral structure observed in the F1 direction more closely the 2D NMR experiment was undertaken using a sufficiently small tl increment, yielding many more resonance lines on a spectrum sliced along the F1 axis. The line distribution had a very unique and interesting structure. To elucidate the line positions theoretically, the signal for the 2D spin-echo experiment performed with any t1 increment was calculated analytically for a homonuclear two-spin-1/2 system undergoing MAS. Virtually six resonance lines (exactly 12 resonance lines) occurred on a spectrum sliced along the F1 axis. In addition, it was demonstrated that the intensities of some resonance lines were largely dependent on the dipolar interaction.