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NMR Noise Spectroscopy

NMR noise spectra depend on the resonance circuit, spin density, relaxation, inhomogeneous broadening, radiation damping and temperature. Although they are power spectra, line shapes are generally mixed absorptive-dispersive. At the conventional tuning optimum (CTO) noise signals should appear as dips in the thermal noise power base line [1]. However, this symmetrical dip line shape is usually found at large tuning o sets from the Larmor frequency, the spin noise tuning optimum, SNTO. At the CTO, often hundreds of kHz from the SNTO, dispersive noise line shapes prevail. Both pure spin noise, from incomplete cancellation of random fluctuations of magnetic moments, and absorbed circuit noise ACN, due to radiation damping [2], contribute to noise spectra. The complex tuning dependence [3] can be attributed largely to ACN. The absorptive pure spin noise contribution can be observed essentially undisturbed in wide line solids spectra [4] and in presence of fi eld gradients [5]. By adjusting probes for SNTO conditions up to 50% increase in sensitivity can be achieved for different types of solid and liquid state experiments [3, 4, 6]. [1] McCoy, M.A. ; Ernst, R.R. Chem Phys Lett 1989, 139, 587. [2] Giraudeau, P. ; Mueller, N. ; Jerschow, A. ; Frydman, L. Chem Phys Lett 2010, 489, 107. [3] Nausner, M. ; Schlagnitweit, J. ; Smrečki, V. ; Yang, X. ; Jerschow, A. ; Mueller, N. J Magn Reson 2009, 198, 73. [4] Schlagnitweit, J. ; Dumez, J.N. ; Nausner, M. ; Jerschow, A. ; Elena-Herrmann, B. ; Mueller, N. J Magn Reson 2010, 207, 168. [5] Mueller, N. ; Jerschow, A. Proc Natl Acad Sci USA 2006, 103, 6790. [6] Nausner, M. ; Goger, M. ; Bendet-Taicher, E. ; Schlagnitweit, J. ; Jerschow, A. ; Mueller, N. J Biomol NMR 2010, 48, 157.

NMR spin noise

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