Experiments in Solids

Combined laser-microwave spectroscopy based on optical pumping was also performed in the solid state. Spectral line broadening caused, e.g., by strain and phonon interaction, can be overcome by extreme cooling and specific site selective procedures. Very narrow lines are attainable particularly in the spectra of rare earth ions doped to crystals in low concentration. Rare earth ions, therefore, play an important role in solid state spectroscopy, as will be illustrated in the course of this section. 

Mollenauer and co-workers used the MCD effect in the absorption band of an F center in order to detect, for the first time, changes in the ground state spin polarization induced by ENDOR in the relaxed excited state. A He-Ne laser served for optical pumping as well as for monitoring the magnetic circular dichroism, while several preceding experiments still had used conventional lamps. The laser beam, which passed a quarter wave plate with a stress modulation frequency of SO kHz, was irradiated onto a KI crystal that contained the F centers under study. The transmitted laser light was monitored with a photomultiplier and processed with lock-in technique. 

In a second experiment,ENDOR measurements were performed in the optically populated excited p5/2 Es/2 state of Tm in Cap2, using the same apparatus. The ENDOR transitions were monitored via the circular polarization of the fluorescence. The authors obtained the ligand hyperfine structure constants A, = 4.83 (3) MHz and Ap = 3.59 (3) MHz of the first shell of fluorine neighbors, thus providing the first ENDOR results of an optically excited state of an impurity center. 

Shelby et al extended the optical detection scheme for solid-state NMR, used by Erickson/to the investigation of rf coherent transients in nuclear hyperfine substates of dilute Pr in LaFs at They observed rf 

In contrast to the previous experiments with dilute rare-earth ions, quadrupole splittings in the ground ( F ) and excited ( Z o) states of Eu in the stoichiometric rare-earth compound EuPsOu were also determined by laser hole burning and optically detected 

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When the polymer was prepared by the suspension polymerization technique, the product was crosslinked beads of unusually uniform size (see Fig. 16 for SEM picture of the beads) with hydrophobic surface characteristics. This shows that cardanyl acrylate/methacry-late can be used as comonomers-cum-cross-linking agents in vinyl polymerizations. This further gives rise to more opportunities to prepare polymer supports for synthesis particularly for experiments in solid-state peptide synthesis. Polymer supports based on activated acrylates have recently been reported to be useful in supported organic reactions, metal ion separation, etc. [198,199]. Copolymers are expected to give better performance and, hence, coplymers of CA and CM A with methyl methacrylate (MMA), styrene (St), and acrylonitrile (AN) were prepared and characterized [196,197]. 

Theoretical Aspects of Microelectrode Experiments in Solid State Ionics... 

Cross-polarization is a well-known method for enhancement of low-/ nuclei signals in solids (CP MAS experiments)145. The theory and first cross-polarization experiment in liquid were presented by Hartmann and Hahn in the same paper that laid the foundation of the famous CP experiments in solids in 196274. It took almost two decades until CP experiments in liquids were investigated in more detail by Ernst and coworkers146 and Bertrand and coworkers147. 

See V.G. Tsirelson and R.P. Ozerov, Electron density and bonding in crystals principles, theory and x-ray diffraction experiments in solid state physics and chemistry, Institute of Physics, Bristol, UK (1996) P. Coppens, X-ray charge densities and chemical bonding. lUCr Texts on Crystallography 4, Oxford University Press, Oxford, New York (1997)... 

P. Mansfield, M. J. Orchard, D. C. Stalker and K. H. B. Richards, Symmetrized multipulse nuclear-magnetic-resonance experiments in solids measurement of the chemical-shift shielding tensor in some compounds. Phys. Rev., 1973, B7, 90-105. 

New isotropic mixing sequences suitable for scalar correlation experiments in solids have been designed using symmetry principles similar to those employed in the construction of the C7 dipolar recoupling sequence. Compared with existing methods, the new isotropic mixing sequences are... 

The principal goal of this project is to demonstrate electrolysis technology using ceramic electrochemical cells based on solid oxide proton conductors. Los Alamos National Laboratory (LANL) has experience in solid-state bulk and thin... 

These remarks also apply to high resolution experiments in solids. VanderHart et al., (1981) have shown that the... 

Cogwheel phase-cycling schemes were applied by Ivchenko et al. to sideband suppression and sideband separation experiments in solid state NMR. It has been shown that cogwheel phase cycles lead to the elimination of most pulse imperfection effects, while using far fewer experimental signal acquisitions than conventional phase-cycling methods. 

The magnetic properties of biradicals in solution have been thoroughly investigated for several decades. Of particular interest in the context of this chapter are high field experiments in solid matrices performed in complement to usual X band [42]. The g-anisotropy has a predominant influence on the spectral shape at 245 GHz of the 1,4-Bis(4",4"-dimethyloxazolidine-3"-oxyl)-cyclohexane biradical. 

Most single molecule experiments in solids at low temperatures described in this book have been performed using fluorescence excitation techniques in which the pure electronic absorption spectrum is monitored by detection of the total Stokes shifted fluorescence as a function of the excitation frequency. There is, however, also the possibility to excite the molecule with a fixed frequency in the maximum of its absorption line and disperse the emitted fluorescence light by a monochromator. In this fashion the vibrationally resolved fluorescence spectrum of a single molecule can be recorded. 

In a conventional optical pumping experiment in solids, an intense pumping beam perturbs the net populations of various atomic or molecular energy levels in a sample, which are then monitored to provide information about the relaxation processes that cause the system to return to its equilibrium state. While this technique is sensitive to the net level populations of the atoms, it is relatively insensitive to processes which preserve net populations while redistributing them spatially through the sample volume, for example by mutual spin flip interactions or reabsorption... 

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