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91.
92.
Yousufuddin M Gutmann MJ Baldamus J Tardif O Hou Z Mason SA McIntyre GJ Bau R 《Journal of the American Chemical Society》2008,130(12):3888-3891
A four-coordinate hydrogen atom has been unambiguously located, by single-crystal neutron diffraction for the first time, in the center of the tetrahedral metal complex Y4H8(Cp')4(THF) [Cp'=C5Me4(SiMe3)]. The core of the molecule consists of a tetranuclear cluster with one interstitial, one face-bridging, and six edge-bridging hydride ligands. The compound was prepared via the reaction of YCp'(CH2SiMe3)2(THF) with gaseous H2. Neutron data were collected on a 4 mm3 crystal at the Quasi-Laue diffractometer VIVALDI at ILL (Grenoble)1a and on an 8 mm3 crystal at the SXD diffractometer at ISIS (Didcot). The final agreement factor is R = 8.9% for 4171 reflections. The existence of 4-coordinate hydrogen now completes the series of high-connectivity hydride ligands located in the interstitial cavities of molecular cluster complexes. We had previously reported the existence of 6-coordinate hydrogen in the octahedral cavity of [HCo6(CO)15]- in 1979, and 5-coordinate hydrogen in the square pyramidal cavities of [H2Rh13(CO)24]3- in 1997, also via single-crystal neutron analyses. 相似文献
93.
Jill Wisnewski Ferguson Timothy J. Dudley Kyle C. Sears Sally M. McIntyre Mark S. Gordon R.S. Houk 《Spectrochimica Acta Part B: Atomic Spectroscopy》2009,64(7):690-696
Several polyatomic ions in inductively coupled plasma–mass spectrometry are studied experimentally and by computational methods. Novel calculations based on spin-restricted open shell second order perturbation theory (ZAPT2) and coupled cluster (CCSD(T)) theory are performed to determine the energies, structures and partition functions of the ions. These values are combined with experimental data to evaluate a dissociation constant and gas kinetic temperature (Tgas) value. In our opinion, the resulting Tgas value can sometimes be interpreted to deduce the location where the polyatomic ion of interest is generated. The dissociation of N2H+ to N2+ leads to a calculated Tgas of 4550 to 4900 K, depending on the computational data used. The COH+ to CO+ system yields a similar temperature, which is not surprising considering the similar energies and structures of COH+ and N2H+. The dissociation of H2CO+ to HCO+ leads to a much lower Tgas (< 1000 to 2000 K). Finally, the dissociation of H2COH+ to HCOH+ generates a Tgas value between those from the other HxCO+ ions studied here. All of these measured Tgas values correspond to formation of extra polyatomic ion in the interface or extraction region. The computations reveal the existence of isomers such as HCO+ and COH+, and H2CO+ and HCOH+, which have virtually the same m/z values and need to be considered in the interpretation of results. 相似文献
94.
JohnA. McCauley MichaelT. Rudd KevinT. Nguyen CharlesJ. McIntyre JosephJ. Romano KimberlyJ. Bush SandorL. Varga CharlesW. Ross StevenS. Carroll Jillian DiMuzio MarkW. Stahlhut DavidB. Olsen TerryA. Lyle JosephP. Vacca NigelJ. Liverton 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2008,120(47):9244-9247
95.
We have investigated the pressure-induced structural phase transition in ReO3 by neutron diffraction on a single crystal. We collected neutron diffraction intensities from the ambient and high pressure phases at P=7 kbar and refined the crystal structures. We have determined the stability of the high pressure phase as a function temperature down to T=2 K and have constructed the (P-T) phase diagram. The critical pressure is Pc=5.2 kbar at T=300 K and decreases almost linearly with decreasing temperature to become Pc=2.5 kbar at T=50 K. The phase transition is driven by the softening of the M3 phonon mode. The high pressure phase is formed by the rigid rotation of almost undistorted ReO6 octahedra and the Re-O-Re angle deviates from 180°. We do not see any evidence for the existence of the tetragonal (P4/mbm) intermediate pressure phase reported earlier. 相似文献
96.
Margaret M. Curtin Carter N. Stewart McIntyre Hubert W. King Allan R. Pratt 《Journal of Non》1997,220(2-3):127-138
Slicate glass surfaces were observed over several weeks in normally humid laboratory air by atomic force microscopy. Auger spectroscopy and lateral force microscopy measurements were also made. Samples in the study include; vitreous quartz, bulk insulation glass, bulk and fibrous textile e-glass, and bulk container glass. Various features developed on these surfaces are consistent with patterns seen in crystal growth from supersaturated solution. Auger spectroscopy reveals the presence of chemically bound carbon and supports the hypothesis that these crystals are alkali and alkali earth carbonate species. The presence of these crystals is expected to affect the bonding of a coating to silicate surfaces. 相似文献
97.
A. Ringbom Klas Elmgren Karin Lindh Jenny Peterson Theodore W. Bowyer James C. Hayes Justin I. McIntyre Mark Panisko Richard Williams 《Journal of Radioanalytical and Nuclear Chemistry》2009,282(3):773-779
Following the claimed nuclear test in the Democratic People’s Republic of Korea (DPRK) on October 9, 2006, and a reported
seismic event, a mobile system for sampling of atmospheric xenon was transported to the Republic of South Korea (ROK) in an
attempt to detect possible emissions of radioxenon in the region from a presumed test. Five samples were collected in the
ROK during October 11–14, 2006 near the ROK–DPRK border, and thereafter transported to the Swedish Defense Research Agency
(FOI) in Stockholm, Sweden, for analysis. Following the initial measurements, an automatic radioxenon sampling and analysis
system was installed at the same location in the ROK, and measurements on the ambient atmospheric radioxenon background in
the region were performed during November 2006 to February 2007. The measured radioxenon concentrations strongly indicate
that the explosion in October 9, 2006 was a nuclear test. The conclusion is further strengthened by atmospheric transport
models. Radioactive xenon measurement was the only independent confirmation that the supposed test was in fact a nuclear explosion
and not a conventional (chemical) explosive. 相似文献
98.
99.
D. Hupfeld W. Schweika J. Strempfer W.A. Caliebe U. Köbler K. Mattenberger G.J. McIntyre F. Yakhou Th. Brückel 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,26(3):273-289
We report on an investigation of the magnetic properties of Gd
x
Eu
1 - x
S mixed crystals with compositions in the range of 0.6 <
x
< 1. For the two samples Gd
0.8
Eu
0.2
S and Gd
0.73
Eu
0.27
S a long-range antiferromagnetic order was observed at low temperatures. Element-specific measurements exhibited a different
temperature dependence of the reduced sublattice magnetisation of the two magnetic species. A model calculation and Monte
Carlo simulations revealed that the different temperature dependence is due to frustration effects. These frustration effects
lead to a breakdown of the long-range order for higher europium contents. For the Gd
0.67
Eu
0.33
S-sample we were able to observe a short-range antiferromagnetic order with correlation lengths of a few 10? with X-ray resonance exchange scattering.
Received 25 April 2001 and Received in final form 3 December 2001 相似文献
100.
Compensation of gradient-induced magnetic field perturbations 总被引:3,自引:0,他引:3
Nixon TW McIntyre S Rothman DL de Graaf RA 《Journal of magnetic resonance (San Diego, Calif. : 1997)》2008,192(2):209-217
Pulsed magnetic field gradients are essential for MR imaging and localized spectroscopy applications. However, besides the desired linear field gradients, pulsed currents in a strong external magnetic field also generate unwanted effects like eddy currents, gradient coil vibrations and acoustic noise. While the temporal magnetic field perturbations associated with eddy currents lead to spectral line shape distortions and signal loss, the vibration-related modulations lead to anti-symmetrical sidebands of any large signal (i.e. water), thereby obliterating the signals from low-concentration metabolites. Here the measurement, characterization and compensation of vibration-related magnetic field perturbations is presented. Following a quantitative evaluation of the various temporal components of the main magnetic field, a digital B0 magnetic field waveform is generated which reduces all temporal variations of the main magnetic field to within the spectral noise level. 相似文献