Distant Dipolar Field Measurements in Laser Polarized 3He Gas

P.P. ZÄNKER, R.H. ACOSTA, L. AGULLES-PEDRÓS, J. SCHMIEDESKAMP, H.W. SPIESS

Tübingen, Alemania

Congreso; 28th Annual Meeting of the Magnetic Resonance Discussion Group of the Society of German Chemists; 2006

Asociación Alemana de Química

Introduction: Since the discovery of intermolecular multiple quantum coherences (iMQCs) in solution NMR due to the distant dipolar field (DDF) of spins, great attention has been paid to this subject [1,2]. Up to now this effect could only be detected in liquids, as the thermal magnetization M0 in gases is not sufficient. By using laser polarized (LP) gases M0 can be increased tremendously. Still, the much higher diffusion coefficient D in gases has to be taken into account, as it is about 5 orders of magnitude larger than in liquids. In this work we present the first measurements of the distant dipolar field in the gas phase by detecting the intermolecular double quantum coherence (iDQC) of LP 3He. Methods: The CRAZED pulse sequence used [3] consists of two RF pulses and two gradient pulses, which work as a DQ-filter. The LP 3He (provided by the Physics Department of the University  of Mainz [4]) was admixed with a buffer gas (SF6) to lower and control the diffusion. Results & Discussion: For the first time iDQCs in gases were detected. The time domain signal was measured with a high SNR in LP 3He, while the remaining SQ signal was suppressed by an appropriate phase cycle. The CRAZED sequence was repeated with varying flip angles of the second RF pulse and the expected maximum at 120° was obtained. The high sensitivity of these iDQCs to diffusion and spatial restrictions open the way to new applications, e.g. in structure determination of porous materials or human lungs, similar to studies that have been performed on model systems for liquids [3].                 [1] W.S. Warren, W. Richter, A.H. Andreotti and S. Farmer, Science 267, 2005-2009 (1993). [2] W. Richter and W.S. Warren Conc. Magn. Res. 12, 396-409 (2000). [3] L.-S. Bouchard and W.S. Warren J. Magn. Reson. 170, 299-309 (2004). [4] E. Ottten Europhysics News 35 No. 1 (2004)