Paramagnetic relaxation spectrum

The value is derived from a zero-field spectrum recorded at 150 K. A q could not be determined at 4.2 K because the compound is in the limit of slow paramagnetic relaxation and the strong unquenched orbital moment forces the internal field into the direction of an easy axis of magnetization. As a consequence, the quadrupole shift observed in the magnetically split spectra results only from the component of the EFG along the internal field and the orientation of the EFG is not readily known dbabh is a bulky N-coordinating amide... 

Representative and spectra are presented in Figures 5, 6, 7, and 8 for the Amax and Monterey samples. The quantitative reference (peak at 0.0 ppm) in each spectrum is hexamethyldisiloxane ((CH3)3-Si-0-Si(0113)3). A paramagnetic relaxation reagent (the paramagnetic relaxation reagents used were either tris(acetylacetonato) iron (III), Fe(acac)3, or tris(acetylacetonato) chromium (III), Cr(acac)3 at concentrations of 2-6 X lO M). was added to decrease spin lattice relaxation times (Ti s) and suppress nuclear Overhauser effects (5). In addition,... 

Fig. 5.—The Effect of Gd + on the C Resonances of the Proton-decoupled, Natural-abundance, K -N.m.r. Spectrum of 6. [The concentration of compound 6 was 168 toM in HjO, pH 7. The vertical gam of the spectra of solutions containing large proportions of paramagnetic, relaxation reagent was increased slightly, so that broadening effects could be clearly observed. (A) Sample contained no Gd , and requited 27,000 accumulations. A linebroadening factor of 2.3 Hz was used during the data processing. (B) Sample contained...

The orthochromite, DyCrOa, is paramagnetic above the Neel temperature of 2-16 K, but at 4-2 K a well-resolved magnetic hyperfine spectrum is seen because of a long paramagnetic relaxation time [107]. The parameters (Table... 

DyaOa contains two distinct Dy sites, but these are not clearly distinguished in the MOssbauer spectrum. The paramagnetic hyperfine spectrum features only slight motional narrowing at 20 K, which implies an unusually long relaxation time [109]. 

The selective reduction of a solvent water resonance can also be achieved in a similar way if the transverse relaxation time of the water protons can be reduced (i.e. the resonance broadened) such that this becomes very much shorter than that of the solutes under investigation. This can be achieved by the addition of suitable paramagnetic relaxation agents (about which the water molecules form a hydration sphere) or by reagents that promote chemical exchange. Ammonium chloride and hydroxylamine have been used to great effect in this way [4,5], as illustrated for the proton spectrum of the reduced arginine... 

Additional substances are sometimes added to the sample solution in order to facilitate measurements or to provide an internal reference for chemical shift or quantitation. Certain experiments benefit from the use of a small amount of a paramagnetic relaxation agent such as chromium(III) acetylacetonate (Secs. II.D.4 and II.G). A chemical-shift reference standard may be added if exact shifts are required. Some quantitative analyses employ an internal spin-counting intensity reference such a standard must not interfere with the sample spectrum. If the reference material is inert, it can be added directly to the sample. If it might react with the sample, the... 

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