High-time resolution studies

Because the same energy can be used to collect QEXAFS spectra and x-ray diffraction (QXRD), the two have become an incredibly powerful tool for doing high-time resolution studies. Although to the best of the authors knowledge, there are no studies directly related to Earth and environmental sciences that utilize this technique, it is appropriate to show an example from the catalysis literature illustrating the technique s potential. 

Hoppe P, Ott U (1997) Mainstream silicon carbide grains from meteorites. In Astrophysical Implications of the Laboratory Study of Presolar Materials. Bematowicz TJ, Zinner E (eds) AlP, New York, p 27-59 Hsu W, Wasserburg GJ, Huss GR (2000) High time resolution by use of the Al chronometer in the multistage formation of CAL Earth Planet Sci Lett 182 15-29... 

The combination of the picosecond single electron bunch with streak cameras, independently developed in 1979 at Argonne National Laboratory [55] and at University of Tokyo by us [56], enabled the very high time resolution for emission spectroscopy. The research fields have been extended to organic materials such as liquid scintillators [55-57], polymer systems [58], and pure organic solvents [59]. The kinetics of the geminate ion recombination were studied [55,57,59]. 

Block and co-workers [35] modified the atom probe to develop a method called pulsed-field desorption mass spectrometry (PFDMS), whereby a short high-voltage pulse desorbs all species present on the tip during a catalytic reaction. The repetition frequency of the field pulse controls the time for which the reaction is allowed to proceed. Hence, by varying the repetition frequency between desorption pulses in a systematic way, one can study the kinetics of a surface reaction [35], In fact, this type of experiment - where one focuses on a facet of desired structure, which may include steps and defects - comes close to one of the fundamental goals of catalyst characterization, namely studying a catalytic reaction on substrates of atomically resolved structure with high time resolution. 

Newton MA, Dent AJ, Fiddy SG, Jyoti B, Evans J. Combining diffuse reflectance infrared spectroscopy (DRIFTS), dispersive EXAFS, and mass spectrometry with high time resolution potential, limitations, and application to the study of NO interaction with supported Rh catalysts. Catal Today. 2007 126 64. 

Hegg, E.L., Ho, R.YN., and Que, L. Jr. (1999) Oxygen activation and arene hydroxylation by functional mimics of a-keto acid-dependent iron(II) dioxygenases, /. Am, Chem. Soc. 121, 1972-1973 Heinen, U., Berthold, T., Kothe, G., Stavitski, E., Galili, T., Levanon, H., Wiederrecht, G., and Wasielewski, M.R. (2002) High time resolution Q-band EPR study of sequential electron transfer in a triad oriented in a liquid crystal, J. Phys. Chem. A 106, 1933-1937... 

Wasielewski, M.R. (2002) High time resolution Q-band EPR study of sequential electron transfer in a triad oriented in a liquid crystal, J. Phys. Chem. A 106,1933-1937 Wasielewski, M.R. (1992) Photoinduced electron transfer in supramolecular systems of artificial photosynthesis, Chem. Rev. 92, 435-461. 

Need instrumentation allowing mechanistic studies with high-time resolution. 

The high time resolution for MHQ allows one to study enzyme or chemical catalytic mechanisms in greater depth than hitherto, simply because more intermediates can potentially be trapped. 

High time-resolution is afforded with energy dispersive diffraction (see above). While systematic errors are problematic, reliable structural refinements are possible for a limited class of experiment. The software and method to enable structure refinement using the Rietveld method and ED powder diffraction data are now well-established (Chen and Weidner 1997, Larson and von Dreele 1986). In a recent study of the partitioning of iron between the olivine and ringwoodite polymorphs of (Mg,Fe)2Si04, energy dispersive data were sufficiently accurate to allow derivation of unit cell volumes... 

The high time resolution of the electric field pulse device turned out to be of advantage for the study of nigericin 36). Unfortunately, this technique could not be applied to the electrically neutral macrocyclic compounds, since it is based on the presence of a dissociation field effect. However, nigericin and murexide do give a dissociation field effect. The rate of complex formation between Na+ and nigericin was found to be as high as that for murexide, i. e. diffusion controlled. 

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