In this work we present multiple quantum solid state NMR experiments to study the many-body dynamics of spin systems.

P.P. ZÄNKER; J. SCHMIDT; J. SCHMIEDESKAMP; R. H. ACOSTA; H.W. SPIESS

Pacific Grove, EEUU

Congreso; 49th ENC - Experimental Nuclear Magnetic Resonance Conference; 2008

The spin echo (SE) phenomenon, which was first discovered by Hahn in 1950 [1], provides the basis of numerous pulsesequences in modern NMR and MRI. The reduction of the SE signal due to spin motion has already been subject of manytheoretical and experimental studies in liquids [2,3]. In gases, however, translational motion can lead to significantfrequency shifts on much shorter timescales, even shorter than the pulse distance. This regime of very fast diffusion inthe gas phase has not been studied yet, although it is of special interest for example in the field of gas MRI. Here, for thefirst time, a detailed theoretical and experimental examination of the SE time-signal under the fast motion in the gasphase is presented [4].The experiments were realized by using hyperpolarized (HP) 3He (provided by the Physics Department of the Universityof Mainz [5]) and a self-constructed gas mixing setup, which allows a precise variation of the diffusion coefficient byadmixing HP 3He with heavier buffer gases at different pressures. The influence of fast motion on the echo formation wasfound to be much more dramatic than in the regimes considered so far. It results in a change of the SE signal in terms ofamplitude, shape and echo position (so-called pseudo SE effect [6]). These effects, which arise from the fast translationalmotion of the spins on the timescale of the experiment, were described by an extension of the Stejskal-Tanner equationto arbitrary times for linear gradients. The more general case of non-linear gradients, where an analytical solution cannotbe easily obtained, was simulated using computer calculations.