Relaxation mechanisms lineshapes

Kramers-Kronig (KK) transformation of the reflection spectra. This provides the optical absorption "(cu) semiexperimentally and allows a thorough analysis of the various relaxation mechanisms creating the absorption lineshape (2.102), (2.111) of an ideal finite crystal in its phonon bath. This method is currently used. However, two major difficulties often obscure the credibility of the results ... 

In general, the quadrupole mechanism is a highly effective means of relaxation. The sign of Q relates to the distribution of charge around the nucleus while its magnitude depends upon several factors. Hius, observed relaxation times can vary over a wide range of values. The effects of the quadrupole relaxation mechanism on NMR lineshapes and linewidths have already been treated in appreciative detail. A very recent theoretical... 

In purchasing a new spectrometer, you should specify the desired frequency(ies) which will be dictated by the magnet available and the nuclei and experiments desired. If at all possible, a spectrometer which can operate over a large frequency range (a factor of 25 or more) should be chosen. This will enable you to study a variety of nuclei under conditions of optimum magnetic field. It also permits the study of relaxation times and lineshapes as a function of frequency. (This is an important method in identifying relaxation mechanisms and in separating different contributions to the line-shape. See III.C.2. and VI.D.l.)... 

In this paper, we report on two experiments which enabled us to improve our understanding of Na and Li lasers. In particular, we obtained assignment of the levels involved in the laser cycles, and evaluation of their lifetimes, relaxation rates and mechanisms, and transition dipole moments. We will also give preliminary results on the experimental study of gain lineshapes, which will ultimately be compared with a theoretical model. 

In Chapter 1, Fyfe, Mueller, and Kokotailo describe the applications of solid-state NMR to the study of zeolite molecular sieve catalysts and related systems. Zeolites provide an apt arena in which to demonstrate the capabilities of modern techniques such as sample spinning, cross-polarization, and multidimensional correlation spectroscopy. In Chapter 2, Karger, and Pfeifer consider the question of molecular diffusion in catalyst systems. Applications of NMR techniques such as imaging, lineshape analysis, relaxation, pulsed field gradient echo spectroscopy, and NMR tracer exchange are described and compared with other, more traditional techniques such as radioactive tracing. In Chapter 3, Haw discusses the use of NMR to probe catalytic processes, showing how the combination of temperature control with novel NMR probes makes it possible to elucidate reaction mechanisms in situ. 

Hirschinger et al [95] also used the anisotropy of spin-lattice relaxation to distinguish the two mechanisms, in this case the relaxation time associated with quadrupolar order, T q. A pulse sequence similar to Figure 8.2(b) was used. Quadrupolar order for the amorphous regions was shown to decay quickly, and for longer values of DE, only crystalline quadrupole order remained. The spectra could be closely simulated by a diffusion model and correlation time of 100 ps. Calculated jump lineshapes possess a central peak that is not present in the experimental data. 

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