Mary spectra

Fig. 3.31 INS spectra of toluene at 20K obtained on TOSCA and at low Q on MARI. MARI spectra at (a) 4000, (b) 2000 and (c) 800 cm" incident energy respectively, the TOSCA spectrum is shown in (d).

Degeneracy in zero field is common for any pairs with hyperfine couplings and results in the strongest line [13,14]. The position of intersection points in nonzero fields depends on the particular set of hfi parameters [15]. For instance, for an even number n > 4 of equivalent nuclei with spin 1/2 the first intersection occurs always in the field H - 3A. The corresponding resonances have been observed in many systems [12]. The next weaker line was observed for tetramethylethylene radical cation [12] and for hexafluorobenzene and perfluorocyclobutane radical anions [16, 17] in experiments on photoionization. It is predicted [18] that resonances can also occur in the fields substantially exceeding the hyperfine ones if there is a difference in radical g-factors. The narrow MARY spectra have so far been recorded only in systems with known ESR spectra in order to demonstrate the phenomenon itself. However, actually, the method can be used to obtain parameters of ESR spectra and identify the unknown short-lived pairs. 

An obvious limitation on the methods discussed in this review is the need for a choice of radical ion pairs with suitable ESR spectra. Actually, this limitation is due to the insufficient time resolution (quantum beats) or sensitivity (MARY-spectra) of available equipment. Improving these characteristics, one can obtain the spectral information about the systems with a more complex set of hyperfine interactions. Therefore, the further development of observation technique is an urgent task. 

Although the effects of spin coherence have been mainly studied using radiation-chemical processes as an example, published are the first works on the MARY spectra of radical ion pairs produced in solutions by photoionization. Probably, there are no principle obstacles to the application of the method of quantum beats to these systems. Interpretation of results is expected to be more simple, in this case, because of the use of monochromatic sources of ionization and the absence of cross recombination effects typical of the ionization track. Another manifestation of spin coherence, observed experimentally but omitted in this review, is the beats induced by resonance microwave pumping [36-38]. The range of applications of this phenomenon for studying spin-correlated radical ion pairs has yet to be outlined. 

Figure 1 (bottom) schematically depicts a typical dependence of radioluminescence intensity under stationary conditions on the external magnetic field (magnetically affected reaction yield curve, or MARY spectrum)... 

Figure 2. A fragment of energy levels diagram (left) and MARY spectrum (first derivative) for (p-terphenyWi4) /(C6F6) radical ion pair (right) [12]. Solid and dotted lines in the diagram correspond to different nuclear configurations.

The importance of P0 in PNS myelin has been clearly demonstrated. In P0 gene knockout experiments in mice [40], severe hypomyelination and a virtual absence of compact myelin in the PNS is observed. In humans, there are two disease states associated with mutations in the P0 gene Charcot-Marie-Tooth type I disease (see Ch. 38) and Dejerine-Sottas disease, both dysmyelinating diseases that exhibit a spectrum of severity depending on the particular mutation. 

During his visit to our department in 1999,1 was quite taken by his interest in the work of synthetic inorganic chemists and spectroscopists. Frank told me he regarded himself as a theoretician for experimentalists, and hence the title of this obituary. His heart beat a little bit faster when shown a beautiful spectrum, and he could communicate this was an integral factor in his success. His series of lectures met with such applause that many entreated him, with much importunity, to write a book on the Jahn-Teller effect. He said he would give serious consideration to the matter. Sadly, this endeavour was never undertaken. In 1997, his intellectual soul-mate Mary O Brien had died. On 13 April 2001, he wrote to me thus, I surely do miss Mary, as I m sure you do too. After her death, I found that my interest in many of the questions we had pursued more or less in parallel simply crashed, and I have not been able to do much to reinvigorate them since. ... 

FIGURE 6.2 Upper plot of the CI2 XS/E of Marie et al. The fitted curve almost superimposes with the experimental and cannot be discriminated. The lower part shows the difference between the experimental and fitted curves. Note that the vertical scale is magnified by about a factor 70. The discontinuities in the lower part (present but not visible in upper part ) show that the experimental spectrum results from a concatenation of adjacent parts of the whole XS. The largest step around 28000 cm represents about 1% of the maximum amplitude. At least five others discontinuities can be seen. When the experimental XS (or XS/E) is smoothed, these discontinuities can hardly be seen. 

Fig. 5. IINS spectrum (MARI, ISIS) at 20 K of activated AI2O3 + 1.12 mmol of CH3OH adsorbed at 300 K. The methyl rock (PCH3), deformation (5CH3), stretch (i CH3), and the rock + deformation combination band (PCH3 + 5CH3) are at 1165, 1454, 2997, and 2614 cm respectively.

Conventional samples are pure compoimds, or mixtures of such, where the only requirement is to measure their INS spectrum at low temperature, irrespective of how exotic they may be. Each INS spectrometer has different requirements in terms of sample shape FANS at NIST uses cylindrical samples, TOSCA at ISIS uses a flat plate and MARI at ISIS uses an annular shape. 

The INS spectrum of rubidium hexahydridoplatinate(IV), Rb2[PtH6], obtained on the direct geometry spectrometer MARI, is given in Fig. 5.10. As anticipated from the considerations presented above the spectrum consists of a series of ridges, all relatively well-defined in energy but broad as a function of Q. The point where the scattering reaches a maximum (as a function of Q) defines the mass-line that joins that point to the origin, for an effective mass, /Weff. 

Fig. 5.10 The INS spectrum of Rb2[PtH]j, taken on a direct geometry spectrometer (MARI, ISIS) [20]. Showing the ridges that are due to the variation of band intensities with momentum and energy transfer.

Fig 5.15 The INS spectrum of Rb2[PtH6] obtained at low momentum transfer (MARI, ISIS), showing the effective suppression of the phonon wing contributions. Reproduced from [20] with permission from the American Chemical Society. 

Fig. 9.18 The INS spectrum (MARI, ISIS) of manganese dioxide, showing the response of a free proton. The horizontal line at 17 A is the line of the cut shown in Fig. 9.19. Reproduced from [68] with permission from Elsevier.

Fig. 11.5 (a) Observed INS spectrum (MARI, ISIS) of sillimanite at 15 K. The estimated one-phonon spectrum is shown by dashed lines, (b) Calculated spectrum broadened to an instrumental resolution of 16 cm", (c) Computed partial phonon density of states of the atoms in the asymmetric unit along x, y and z in sillimanite. Reproduced from [10] with permission from the American Physical Society. 

Fig. 11.10 INS spectrum of graphite derived from the dispersion curves of Fig. 11.9 (dashed line) compared with the experimental spectrum as recorded on TOSCA (lower solid line) and MARI (upper solid line).

Marie A., Fournier, F., and Tabet, J. C., Characterization of Synthetic Pol5rmers by MALDI-TOF/MS Investigation into New Methods of Sample Target Preparation and Consequence on Mass Spectrum Finger Print, Anal. Chem., 72, 5106, 2000. 

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