Resonance linewidth, concentration

The more recent EPR measurements of Nagel et al. (1973) on (Ag, Au)Yb alloys were analyzed for the temperature dependence of the resonance linewidth where a resonance was observed. No resonance signal was detected for Au concentrations <70 at.%, but in varying the Au concentration from 100 to 70 at.%, can be inferred to double while the g factor changes continuously from 3.34 to 3.22. 

An ESR study of the concentration dependence of the fully narrowed resonance linewidth in the hexaborides M jEui cB6 (M=Sr or La) in a wide concentration range 0exchange between Eu -ions is due to the presence of free carriers (indirect exchange via the RKKY-interaction), although a straightforward application of the RKKY-theory gives only qualitative agreement with the experimentally observed AH x) curves. In the lanthanum compoimds, the concentration dependence of... 

Similarly to the ESR of the lanthanide ions in insulators, in metallic systems ESR contributes to understanding of the spectroscopic state of the ion in the host lattice and the symmetry and magnitude of the crystalline electric field at the lanthanide site. The g-shift of the resonance may be related to the sf exchange interaction and the spin polarization of the conduction electrons, and the temperature and concentration dependence of the g-shift and resonance linewidth relate to the bottleneck effect in the spin relaxation process. These relationships have been outlined in section 3.5. 

These values show some dependence on concentration, pH and temperature. Note also the much smaller linewidth for the central, symmetrically 4-coordinated Al atom of the tridecameric AI13 species when compared with that of the twelve less symmetrically coordinated octahedral Al atoms, and the possibility of extracting a reasonably precise value of for this latter resonance which has a linewidth of some 8000 Hz. 

As in the case of the concentration dependence of the chemical shift, the H and 13C band shapes of the surfactant resonance peaks are also concentration dependent. Analysis of H NMR band shapes for large aggregates of a cetyl trimethyl ammonium bromide-water system results in a CMC of 1.0 mM this is consistent with the value measured by other methods.57 The H NMR bands of alkyl trimethyl ammonium salicylate and hexadecyl pyridinium salicylate aqueous systems start to broaden at concentrations just above the CMC. The broadening continues up to a concentration above which the band shape is almost constant, as the concentration is further increased.-58 I3C NMR linewidth analysis of sodium octanoate in aqueous solution gives reasonable estimated CMC values.59... 

Figure 13(b) shows a JH—15N HSQC spectrum acquired from 0.5 mmol l-1 sample of a 41-residue peptide toxin from the spider Agelena orientalis. The toxin was produced recombinantly and uniformly labeled with 15N. This HSQC spectrum was collected in 30 min, compared with the 12 h required to acquire a natural abundance spectrum from an unlabeled sample of equivalent concentration (see Figure 11). The HSQC, together with the related heteronuclear multiple quantum coherence (HMQC)54 experiment, forms the cornerstone of a wide range of 2D, 3D, and 4D experiments that are designed to facilitate sequence-specific resonance assignment and determination of protein structure. Note that the HSQC technique is the technique of choice for correlation of H and 15N shifts due to generally narrower linewidths in the 15N dimension.55,56 Furthermore, because these and most of the other heteronuclear experiments described below are designed to observe amide protons, the sample must be in H20 (rather than D20). Consequently, a means of suppressing the H20 resonance is required (for details see Section 9.09.2.6).

Most likely the earliest solution work reported was a study of linewidth measurements of the Cu resonance signal in concentrated hydrochloric acid solution containing cuprous and cupric chloride. These studies afforded reasonable calculations for the bimolecular rate constant for the equilibrium electron-exchange process (Eq. 1) ... 

After protons, C is the most widely detected nucleus in NMR. Proton cross-polarization and decoupling are usually applied to increase the S/N, and these types of experiment can result in substantial sample heating. Many forms of C-based NMR thermometers have been proposed. The first such system was based on the cis-trans conformational equilibrium of furfural, with the linewidths of carbon-3 and the aldehyde carbon being temperature-dependent. There are many disadvantages of linewidth-based measurements, and subsequent developments concentrated almost wholely on temperature-dependent C chemical shifts. The first such system utilized a temperature-dependent lanthanide-induced pseudocontact shift in a complex of acetone-de and ytterbium(III)1,1,1,2,2,3,3-heptafluoro-7,7-dimethyl-4,6-octadionate (Yb (fod)3). The 6co of the acetone-dg, measured with respect to a CS2 standard, was almost linearly dependent on 1 / T with a small quadratic term over a range 200-315 K. If a small amount of protonated acetone was added, then the proton resonance, measured with respect to the protons of TMS, was also found to be temperature dependent ... 

If the energies of Frenkel and Wannier-Mott excitons are in resonance the size of the hybrid state is comparable with that for Wannier-Mott excitons, i.e. it is much larger than the radius of Frenkel excitons. In this case we can expect that the saturation concentration of excitons in hybrid structure will be of the same order as in a semiconductor quantum wire. Outside the resonance range, the coupling is governed by the parameter T2/(Ep — Ew) and is rather small. The condition of resonance is rather strict for the considered range of parameters and requires a careful choice of materials for both wires. And, naturally, the exciton linewidths should be small compared to 2Y. For these parameters these linewidths have to be smaller than the resonant splitting 2T 11 meV of the hybrid excitations. 

---