Electron linewidth

High-resolution spectroscopy used to observe hyperfme structure in the spectra of atoms or rotational stnicture in electronic spectra of gaseous molecules connnonly must contend with the widths of the spectral lines and how that compares with the separations between lines. Tln-ee contributions to the linewidth will be mentioned here tlie natural line width due to tlie finite lifetime of the excited state, collisional broadening of lines, and the Doppler effect. 

The negative sign in equation (b 1.15.26) implies that, unlike the case for electron spins, states with larger magnetic quantum number have smaller energy for g O. In contrast to the g-value in EPR experiments, g is an inlierent property of the nucleus. NMR resonances are not easily detected in paramagnetic systems because of sensitivity problems and increased linewidths caused by the presence of unpaired electron spins. 

SWCNTs have been produced by carbon arc discharge and laser ablation of graphite rods. In each case, a small amount of transition metals is added to the carbon target as a catalyst. Therefore the ferromagnetic catalysts resided in the sample. The residual catalyst particles are responsible for a very broad ESR line near g=2 with a linewidth about 400 G, which obscures the expected conduction electron response from SWCNTs. 

The XRD peaks characteristic of Co and Ni disappeared after the treatment, as did the broad ESR line, successfully leaving only the narrow asymmetric line with 26 G linewidth as shown in Fig. 8 [40]. The g-value of the narrow line is =2.002 0.001. The narrow ESR line shows Dysonian at all temperatures in the range of 4-300 K. Furthermore, the ESR intensity is quite independent of T and thus the density of conduction electrons is invariant as a function of temperature as shown in Fig. 9. These show that the material is highly metallic, even at low 7. 

These nuclei (and they form by far the majority of the NMR-active nuclei ) are subject to relaxation mechanisms which involve interactions with the quadrupole moment. The relaxation times Tj and T2 (T2 is a second relaxation variable called the spin-spin relaxation time) of such nuclei are very short, so that very broad NMR lines are normally observed. The relaxation times, and the linewidths, depend on the symmetry of the electronic environment. If the charge distribution is spherically symmetrical the lines are sharp, but if it is ellipsoidal they are broad. 

The second two terms in (5) are called T-terms or two-photon terms , which have (Qe g — 2hco) in the denominator corresponding to the excitation of an electron into the higher-lying excited state e. If we consider a resonance condition where hco = hcoeig/2 and assume that the transition linewidth is narrow, rt>s, < < h coeg imaginary part of the T-term can then be expressed in SI units as ... 

It is also possible to form radical cations and radical anions on the same alumina or silica-alumina surface (88). One of the more interesting observations was that a marked enhancement of the radical anion spectrum for trinitrobenzene results when perylene is adsorbed on an alumina surface, and similarly the radical cation signal is reenforced by adsorption of trinitrobenzene. The linewidths of the spectra confirm that the radical ions are separated by a distance greater than 10 A. This means that the electron must be transfered through the lattice or that the ions separate after the transfer step, which seems unlikely. Oxygen was still required for the formation of the radical cation. 

Hagen, W.R. 1981. Dislocation strain broadening as a source of anisotropic linewidth and asymmetrical lineshape in the electron paramagnetic resonance spectrum of metal-loproteins and related systems. Journal of Magnetic Resonance 44 447-469. 

Scalar (J) interactions between nuclei are transmitted indirectly through the electrons of the bonds. In the solid state, the effects of J couplings are usually obscured by the dipolar, chemical shift, and quadrupolar contributions to the linewidth. Nevertheless, the measurement and utilization of J couplings are possible even if... 

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