Showing papers by "Juergen Eckert published in 1995"

Crystal Structure of Acetanilide at 15 and 295 K by Neutron Diffraction. Lack of Evidence for Proton Transfer along the N-H.cntdot..cntdot..cntdot.O Hydrogen Bond

Abstract: The crystal structure of acetanilide C{sub 8}H{sub 9}NO, M{sub r} = 135.17, orthorhombic, space group Pbca, Z=8, has been determined from neutron diffraction data at 15 and 295 K. The crystal data obtained are presented. This new investigation of the structure of acetanilide has been undertaken in order to assess a recent suggestion that confirmational substates in the amide proton position may be responsible for the vibrational anomalies. We found no evidence for multiple conformations or transfer along the N-H...O hydrogen bond of the amide proton at either temperature. However the intramolecular O...H6 distance from O to the nearest phenyl ring proton is unusually short and the amide proton has relatively close contacts with one of the phenyl and one of the methyl protons, which may well affect the vibrational parameters of the respective molecular groups. 44 refs., 6 figs., 5 tabs.

Inelastic Neutron Scattering Studies of IrIH2(H2)(PPri3)2 and Neutron Diffraction Structure Determination of IrIH2(H2)(PPri3)2.cntdot.C10H8: Implications on the Mechanism of the Interconversion of Dihydrogen and Hydride Ligands

Abstract: We have now determined the molecular structure of IrIH{sub 2}(H{sub 2})(PPr{sup i}{sub 3}){sub 2} {center_dot} C{sub 10}H{sub 8} (2{center_dot}C{sub 10}H{sub 8}) through a single-crystal neutron diffraction study and carried out lNS studies on this complex. We report the result of these studies and their implications on the mechanism of dihydrogen/hydride interchange in the IrXH{sub 2}(H{sub 2})(PPr{sup i}{sub 3}){sub 2} complexes. Our results suggest that the interconversion of dihydrogen and hydride ligands in the IrXH{sub 2}(H{sub 2})(PPr{sup i}{sub 3}){sub 2} complexes is coupled to rotation of the dihydrogen ligand. Limbach et al. have proposed that the mechanism of hydride interchange in transition-metal trihydrides involves the rotation of an intermediate dihydrogen ligand. While it is not clear at this point if dihydrogen/hydride interconversion in the IrXH{sub 2}(H{sub 2})(PPr{sup i}{sub 3}){sub 2} complexes involves a bis(dihydrogen) intermediate, our results suggest that this process does not involve initial weakening of the dihydrogen H-H bond. 20 refs., 2 figs., 1 tab.

Comment on ''Dynamical Test of Davydov-Type Solitons in Acetanilide Using a Picosecond Free-Electron Laser''

Abstract: A Comment on the Letter by Wunshain Fann, {ital et} {ital al}., Phys. Rev. Lett. {bold 64}, 607 (1990).

Monte Carlo study of the performance of a time-of-flight multichopper spectrometer

Abstract: The Monte Carlo method is a powerful technique for neutron transport studies. While it has been applied for many years to the study of nuclear systems, there are few codes available for neutron transport in the optical regime. The recent surge of interest in so-called next generation spallation neutron sources and the desire to design new and optimized instruments for these facilities has led us to develop a Monte Carlo code geared toward the simulation of neutron scattering instruments. The time-of-flight multichopper spectrometer, of which IN5 at the ILL is the prototypical example, is the first spectrometer studied with the code. Some of the results of a comparison between the IN5 performance at a reactor and at a Long Pulse Spallation Source (LPSS) are summarized here.