Synchrotron Subject

Fe-S and Fe-Fe distances in [2Fe-2S], [3Fe-4S], and [4Fe-4S] clusters are all very similar 2.3 and 2.7 A, respectively. In the [6Fe-6S] prismane model cluster, however, there is an additional Fe-Fe distance at 3.7 A (Fig. 2). If a [6Fe-6S] cluster were present in the Fepr protein, then this longer Fe-Fe distance should he visible with extended X-ray absorption fine structure (EXAFS). As a consequence, EXAFS studies were carried out at the CCLRC Synchrotron Radiation facility in Daresbury, UK. The two Fepr proteins (those of D. vulgaris and D. desulfuricans), as well as a synthetic [6Fe-6S] cluster, were subjected to an EXAFS study. Low-temperature EXAFS... 

Frozen solution of deoxymyoglobin (Mb) has been the subject of an NFS investigation in the temperature range 3.2-230 K (Fig. 9.6) [15]. The synchrotron pulses were transmitted through the entrance window of the sample with a size of 12 mm 2 mm (width height). By scanning the sample area with a narrow beam (about 1 mm 0.3 mm), the homogeneity of the effective thickness was determined as 2.5%, which is more than ten times better than in the aforementioned case. 

XAFS spectroscopy has been used frequently to determine the oxidation state of an element as a catalyst is subjected to treatments such as reduction, oxidation, or exposure to some reactant. It is the near edge of the X-ray absorption spectrum, the XANES region that is usually used for these measurements. As mentioned in the introduction, the first to recognize the value of XANES for this type of investigation was van Nord-strand (1960), and his report appeared well before the advent of synchrotron radiation sources. 

Powdered samples of CbAsFb, CioAsFb and fluorinated CioAsFs were subjected to X-ray absorption spectroscopy utilizing the high intensity X-ray source available at the Stanford Linear Accelerator Synchrotron Facility. The samples were housed in air tight Teflon-gasketed containers provided with... 

The operating cost of synchrotron radiation depends on the subsequent use of the results. For a non confidential study beam time is allocated subject to scientific approval of the project. Use for confidential studies is generally charged for. The amount, which varies between installations can be as much as several thousand euros per day. The analysis time may vary... 

The following results relative to Pd growth on Ni(llO) are the fmit of experiments combining many surface science techniques LEED, STM, AES, XPS, LEIS. It has been also the subject of recent investigations by grazing incidence X-ray diffraction, using synchrotron radiation facilities at ESRF (Grenoble), and by DFT theoretical calculations. 

We compared FTIR spectra of the frozen sample to MeOH at ambient conditions. The results are shown in Figure. 15. When pure methanol is loaded to 5 GPa the ensuing temperature induced reaction proceeds without forming bubbles. We have studied each reproducible reaction process and have determined from FTIR experiments conducted at the National Synchrotron Light Source at Brookhaven National Laboratory (Beam Line U2a) that pure MeOH reacts to form water and carbon dioxide. Methanol subjected to 532nm and 1064 ran 100 ps pulses reacts to form supercritical water, carbon dioxide, ethane, and perhaps methane (see Figures 15, 16, and 17). These same products are predicted by the CHEETAH thermo-chemical code if no carbon, in the form of diamond, is produced. 

All these features explain why the applications of EXAFS to the study of very dispersed materials have increased so much in the last few years. Figure 2 shows the tremendous growth of the number of papers on catalysits characterization by EXAFS coupled to the use of synchrotron light. This figure comes from the very detailed and exhaustive review Bart and Vlaic recently published on the subject... 

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