Single crystal irradiation

In the examples presented below there are figures of strong ENDOR signals obtained from single crystals irradiated and examined at helium temperatures. One must not get the idea that it is easy to obtain ENDOR signals from every sampled examined. Often there are conditions present involving the electronic and nuclear relaxation terms that preclude ENDOR detection even with 100 s of watts of rf power. The conditions that must be met to obtain ENDOR signals are covered in the standard textbooks [26],... 

Figure 6. Dependence of the concentration of paramagnetic centers N at T = 30 K (full symbols) and of the intensity of thermoluminescence (curves 3,4) on the temperature of annealing of the ZnO single crystal irradiated with protons (E = 7.7 MeV. Tjose lO protons/cm ) 1) F -centers 2) paramagnetic states Lizn" 3 and 4) the intensity of thermoluminescence at A, = 6000 and 7200 A (the excitation hv = 2.6 eV).

Figure 2. ESR spectra of MDMA single crystal irradiated at 77 K to 5.34 Mrad and heat-treated for 5 min at 195 K. The magnetic field is parallel to the < axis in the b c plane, and recorded at 77 K (a), 183 K (b), 213 K (c), and 243 K (d). Spectra b, c, and d were measured after heating to the respective temperature for 20 min. Sensitivity of the instrument was kept constant except for the measurement...

From studies of cytosine monohydrate single crystals irradiated at 10 K Sagstuen et al. concluded that the primary reduction product is the N3 protonated anion (Radical Rl). ENDOR experiments detected the C6-H hyperfine coupling, the N3-Hj, hyperfine coupling and one of the small couplings to the N4-H2 protons (see Table H)." ... 

Kg. 41. Critical current densities (W c) as a liinction of field in an Y-123 single crystal irradiated with 580 MeV Sn ions to various fluences (expressed by the matching fields B ) (a) 5K, (b) 77 K. For comparison, the largest y s obtained by proton irradiation of a similar crystal are shown by the dotted lines (Civale 1997). 

Fig. 43. Effects of heavy-ion irradiation under different angles on flux pinning in Y-I23 superconductors (a) hysteresis loops at (top) 5 K and (bottom) 70 K of an Y-123 single crystal irradiated with 580 MeV Sn ions under an angle of 30° with respect to the c-axis and measured with the field at +30° or -30° from the c-axis (cf. the schematic of the field and track orientations, from Civale 1997) (b) angular dependence of the transport critical current densities in Y-123 thin films irradiated under various angles with respect to the c-axis (top parallel to the c-axis, 340 MeV Xe middle 30°, 770 MeV Pb bottom 60°, 340 MeV Xe from Kraus et al. 1994b) (c) angular dependence of the transport critical current densities in an Y-123/Pr-123 multilayer system irradiated by 770 MeV Pb ions under an angle of 30° with respect to the c-axis (Kraus et al. 1994b).

Wark, Whitlock, and co-workers [72]-[75] extend these ideas in shock compression of < 111 >-oriented silicon single crystals. The method of producing the shock wave differs from previous X-ray diffraction studies, but the basic concepts are the same. Higher X-ray fluences result in a time resolution of 0.05-0.1 ns. This permits a sequence of exposures at various irradiances and delay times, thus mapping the interatomic spacing of the shock-compressed surface as a function of time. 

The photo-Kolbe reaction is the decarboxylation of carboxylic acids at tow voltage under irradiation at semiconductor anodes (TiO ), that are partially doped with metals, e.g. platinum [343, 344]. On semiconductor powders the dominant product is a hydrocarbon by substitution of the carboxylate group for hydrogen (Eq. 41), whereas on an n-TiOj single crystal in the oxidation of acetic acid the formation of ethane besides methane could be observed [345, 346]. Dependent on the kind of semiconductor, the adsorbed metal, and the pH of the solution the extent of alkyl coupling versus reduction to the hydrocarbon can be controlled to some extent [346]. The intermediacy of alkyl radicals has been demonstrated by ESR-spectroscopy [347], that of the alkyl anion by deuterium incorporation [344]. With vicinal diacids the mono- or bisdecarboxylation can be controlled by the light flux [348]. Adipic acid yielded butane [349] with levulinic acid the products of decarboxylation, methyl ethyl-... 

This reaction was proven to proceed in a partial single crystal-to-single crystal manner [35, 36]. However, irradiation of a 1 1 complex of 10c with 154 gave (+)-155 of 95% ee in 29% yield [37].By a similar method, 156,158,and 160 gave... 

The ESR spectrum of methanesulfinyl radical (CH3SO), identified in a y-irradiated single crystal of dimethyl sulfoxide , indicates that the unpaired electron resides essentially (72%) on the sulfur 3p orbital with modest population on the sulfur 3s (0.65%) A detailed analysis of the temperature dependence leads to 2.6 kcal mol barrier height for the hindered internal rotation of the methyl group. At low temperature (88 K) the radical adopts a fixed conformation in which one proton lies in the nodal plane of the sulfur 3p orbital however, it was not possible to distinguish either experimentally or by ab initio SCF-MO calculations between the two possible conformations, that is, 2 and 3. 

As a rutile TiOg single crystal is irradiated with UV light in a AgNOg solution, silver nanoparticles are deposited and grown gradually (Figure 3). 

When a nanoporous Ti02 film consisting of Ti02 nanoparticles is used instead of the single crystal, the extinction band of silver nanoparticles deposited by UV-irradiation is much broader. This is probably because the nanopores in the Ti02 film mold the silver nanoparticles into various anisotropic shapes [9], although direct observation of the particles in the nanopores is difficult. 

Figure 6. Difference extinction spectra of the silver nanoparticles on the rutile XiO2(100) single crystal after irradiation with monochromatic visible light (wavelength = 480 nm, light intensity 5.0mW cm , irradiation time = 30 min 550 nm, 5.0mW cm , 30min 600nm, 3.0mWcm , 60min (FWHM = lOmn)).

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