The first observation of Carbon-13 spin noise spectra

We demonstrate the first C-13 NMR spin noise spectra obtained without any pulse excitation by direct detection of the randomly fluctuating noise from samples in a cryogenically cooled probe. Noise power spectra were obtained from C-13 enriched methanol and glycerol samples at 176 MHz without and with decoupling, which increases the sensitivity without introducing radio frequency interference with the weak spin noise. The multiplet amplitude ratios in H-1 coupled spectra indicate that, although pure spin noise prevails in these spectra, the influence of absorbed circuit noise is still significant at the high concentrations used. In accordance with the theory heteronuclear Overhauser enhancements are absent from the H-1-decoupled C-13 spin noise spectra. (C) 2012 Elsevier Inc. All rights reserved.