• Summary

NM140015E

Nitrogen-14 has a spin quantum number of I = 1. Besides the allowed single-  quantum transitions between Iz = 0 and Iz = +/- 1, there is a forbidden transition  between Iz = +1 and -1. This transition is weakly allowed in the presence of  quadrupolar couplings and can be excited by the rf-field with either the Larmor  frequency (DQ: double quantum transition) or the twice of the Larmor frequency  (OT: overtone transition). Here we show 1H-14N OT correlation spectra can easily be  observed by 1H-14N OT HQMC experiments at ultrafast MAS rate. Since 14N OT is  free from the first order quadrupolar broadening, the line shape are relatively  narrow and affected only by 2nd order quadrupolar broadening. Although there still  remain several issues in 14N OT spectroscopy, such as limited bandwidth, small  transition moments, 14N OT spectroscopy opens a new world for us!

14N OT filtering efficiency at various spinning rates, 1H-14N OT HMQC spectrum of glycine at 90 khz MAS

Reference

Y. Nishiyama, M. Malon, Z. Gan, Y. Endo, T. Nemoto, J. Magn. Reson. 230 (2013) 160-164.

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