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11.
12.
Intermediate scattering functions for density fluctuation in D2O contained in pores of a Vycor glass have been measured using an improved neutron spin-echo spectrometer at two supercooled temperatures. The measurements cover the time range from 1 to 2300 ps with the Q range spanning the first diffraction peak of water. The time correlation functions can be fitted to a stretched exponential relaxation function with a Q-dependent amplitude. Both the stretch exponent and the relaxation time peak approximately at the Q value corresponding to the first diffraction peak, confirming the validity of the mode coupling idea in supercooled water. 相似文献
13.
Structure of supercritical water 总被引:2,自引:0,他引:2
M. -C. Bellissent-Funel 《Journal of Molecular Liquids》2001,90(1-3):313-322
This review paper gives the more up to date information on the structure of supercritical water, at different thermodynamic states, for densities ranging from 0.2 to 0.7 g.cm−3, studied by neutron scattering. The experimental partial pair correlation functions gOH(r), GHH(r) and gOO(r) are compared with the results of molecular dynamics simulations using the (SPCE) model potential for water. The results confirm that hydrogen bonding is still present in dense supercritical water and are in good agreement with data obtained by NMR and Raman spectroscopies. 相似文献
14.
Frédérick Adam Didier Thiébaut Fabrice Bertoncini Marion Courtiade Marie-Claire Hennion 《Journal of chromatography. A》2010,1217(8):1386-1394
This paper reports the conditions of online hyphenation of supercritical fluid chromatography (SFC) with twin comprehensive two-dimensional gas chromatography (twin-GC × GC) for detailed characterization of middle distillates; this is essential for a better understanding of reactions involved in refining processes. In this configuration, saturated and unsaturated compounds that have been fractionated by SFC are transferred on two different GC × GC columns sets (twin-GC × GC) placed in the same GC oven. Cryogenic focusing is used for transfer of fractions into the first dimension columns before simultaneous GC × GC analysis of both saturated and unsaturated fractions. The benefits of SFC–twin-GC × GC are demonstrated for the extended alkane, iso-alkane, alkene, naphthenes and aromatics analysis (so-called PIONA analysis) of diesel samples which can be achieved in one single injection. For that purpose, saturated and unsaturated compounds have been separated by SFC using a silver loaded silica column prior to GC × GC analysis. Alkenes and naphthenes are quantitatively recovered in the unsaturated and saturated fractions, respectively, allowing their identification in various diesel samples. Thus, resolution between each class of compounds is significantly improved compared to a single GC × GC run, and for the first time, an extended PIONA analysis of diesel samples is presented. 相似文献
15.
Tandon SS Dul MC Lee JL Dawe LN Anwar MU Thompson LK 《Dalton transactions (Cambridge, England : 2003)》2011,40(14):3466-3475
Ligands based on carbo- and thio-carbohydrazone cores, modified with pyridine, carboxylate and oxime ends, have been examined. They display a tautomeric versatility based on the flexible nature of the hydrazone linkages, leading to varied coordination motifs. Examples of mononuclear (Co(II), Ni(II)), dinuclear (Co(III)), 1D chain (Cu(II)) and square [2 × 2] grid (Ni(II)) complexes are obtained. Ferromagnetic (Cu(II)) and antiferromagnetic (Ni(II)) exchange is observed, with spin coupling in the Ni(II)(4) square grids propagated through the μ-O and μ-S bridges. Weak antiferromagnetic exchange (J = -6.0 cm(-1)) is observed for the μ-O bridged grid, despite the large Ni-O-Ni angles (137-141°), while for the μ-S bridged grids much stronger exchange is observed (J = -148 cm(-1), -198 cm(-1)). This is much larger than expected based on the Ni-S-Ni bridge angles (151-169°), and is associated with the soft (less polarizing than oxygen) nature of the sulfur bridge, which would allow for much more efficient transmission of spin exchange than observed in the μ-O bridged case. Structures and variable temperature magnetic data are included, and spin exchange is analyzed using normal Heisenberg exchange models. No examples involving oxime (NO) bridging are reported, which reflects the positioning of the N,O and N,S donor combinations in each ligand, and the preferred coordination through these donor atoms. 相似文献
16.
Neutron diffraction techniques used in the study of the structural characteristics of liquid water under ambient conditions are reviewed, showing the way that developments in the experimental and analytic procedures have led to improvements in the extracted results. The three partial pair correlation functions (OH, HH and OO) can be isolated from a set of diffraction measurements with varying hydrogen/deuterium isotopic composition. Although isotopic substitution is used routinely in many other investigations there are particular difficulties with hydrogenous systems due to the high incoherent scattering from hydrogen and the possibility that the H/D substitution is not a true isomorphic replacement. These features are discussed in some detail to analyse the systematic errors and the precision of the final results. An additional aspect of the comparison of data taken by different groups concerns the use of either reactor or pulsed neutron methods. Studies using the Orphee reactor with an over-determined set of five datasets are considered in detail, using analytic correction procedures based on the Powles formalism. Various consistency checks are applied to the data such that smoothing or iteration routines are not required. Two independent sets of the OD and DD pair correlation functions are obtained and are compared with the latest results from Soper et al. The small discrepancies between the various datasets are discussed in terms of propagating systematic errors and also possible variations from H/D equivalence. The relevance of the new results for the interpretation and modelling of ambient water structure are presented and the review ends with a brief comment on likely future developments that incorporate additional experimental information. 相似文献
17.
18.
Marie-Claire Lasne Jean-Louis Ripoll Jean-Claude Guillemin Jean-Marc Denis 《Tetrahedron letters》1984,25(35):3847-3848
5,6-dihydropyridine 1 is synthesized either by flash vacuum thermolysis of 1-azabicyclo[2.2.2] oct-2-ene 3 or by dehydrochlorination over solid bases of N-chloro-1,2,5,6-tetrahydropyridine 4 and characterized at low temperature by its 1H and 13C nmr and ir spectra. 相似文献
19.
Kittaka S Takahara S Yamaguchi T Funel MC 《Langmuir : the ACS journal of surfaces and colloids》2005,21(4):1389-1397
The dynamics of water molecules in the layered vanadium pentoxide hydrate, V(2)O(5).nH(2)O, were studied by quasi-elastic neutron scattering (QENS) measurements. Heterogeneity of the dynamic properties was confirmed by alpha-relaxation model analysis. Translational diffusion of monolayer and double-layer water molecules is by site-to-site diffusion and is reduced relative to that of bulk water. Water molecules lose their mobility markedly and solidify with decreasing temperature. However, mobile water remains at 253 K. Rotational diffusion coefficients are unaffected by confinement and are very similar to the bulk values determined at temperatures in the range 253-298 K. The dynamic speed characterized by QENS is much faster than that expected from the data determined by deuterium NMR (DNMR) measurements at low temperatures. 相似文献
20.
M.P. Fontana P. Migliardo M.C. Bellissent-Funel R. Kahn 《Solid State Communications》1980,36(6):541-543
We have studied saturated solutions of ZnCl2 (and NiCl2) in D2O by time-of-flight quasi-elastic and inelastic neutron scattering spectroscopy. Spectra were taken at room temperature as a function of transferred momentum. We find that ionic diffusion in these solutions is best described by a crystal vacancy diffusion model. We also find evidence of collective excitations in the region of ~ 20 meV. 相似文献