Graphitic single-crystal analysis

The three dimensional structure was obtained by means of single crystal X-ray diffraction. CuKa radiation, a graphite monochromator, and a photomultiplier tube were used to collect 1825 total reflections on an automated diffractometer. Of these, 1162 were used for the analysis. Figure 2 shows a computer generated drawing of halcinonide. The position of the chlorine atom was not clear from the Patterson map, but the direct method program "MULTAN" gave its position. 

The structure of etodolac has been established by single crystal X-ray diffraction analysis [9]. Crystals of racemic etodolac were obtained by recrystallization from benzene-petroleum ether. A small brick shaped sample having approximate dimensions 0.2 x 0.2 x 0.3 mm was used for collecting three dimensional intensity data on a computer-controlled Picker FACS-I four circle diffractometer with a graphite monochromator. 

The methanation reaction (3H2 + CO — CH4 + H20) has been thoroughly studied by Goodman and co-workers (4, 5, 71, 96) over Ni single crystals. Since the specific rates, activation energies, and pressure dependencies are very similar over Ni(100), Ni(lll), and AI203-supported Ni, the reaction is structure insensitive (71, 96). Transient kinetic studies at medium pressures combined with postreaction AES analysis on Ni(100) have identified a carbidic form of adsorbed carbon as the reaction intermediate, and graphitic carbon as a poison formed at higher temperatures (71, 96). 

Colorless single crystals of P7[Si(SiMe3)3]3 suitable for X-ray diffraction (Fig. 3) analysis were grown in benzene. The data collection [4] was performed under a stream of N2 at -70°C using a Siemens diffractometer with a CCD SMART detector and graphite monochromated molybdenum K radiation (k = 0.71073 A). The crystal was mounted on the tip of a glass fiber in inert oil. 

X-ray diffraction is a useful analytical technique to determine the changes in structure that occur during graphitization. A detailed analysis of this technique is given in Ref. 14. As with all crystalline materials, a sharp diffraction pattern is obtained with single-crystal graphite. This pattern is schematically shown in Fig. 4.5.PJ Pronounced crysteillinity is indicated by the development of the 002, 004 and 101 peaks. 

Returning to the problem of the surface chemical-state analysis of supported metal catalysts note that the particle size dependence of the BE should be known, or at least a reliable trend in it. There are different multitechnique ways of measuring it. The metal of interest can be evaporated or sputtered onto a flat substrate, for instance an oxidized Si wafer, a sapphire single crystal or pyrolytic graphite. Mean particle-size-related submonolayer coverages can then be estimated by quantitative XPS [36,37]. More directly, STM has been used to... 

Once coarsening and recrystallization stops, graphite flakes will preserve isotope composition due to slow diffusion. Intracrystalline zoning of 5 C has been detected in some crystals by most studies that have evaluated it. This has been demonstrated by delamination of single flakes at the 20-100 pm-scale (Wada 1988, Arita and Wada 1990, Kitchen and Valley 1995, Satish-Kumar 2000), by ion microprobe (Farquar et al. 1999) or, more simply, by analysis of large vs. small flakes from the same rock (Kitchen and Valley 1995). 

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