A neutron-diffraction study on the structural relationships of RCo5 hydrides

The hexagonal RCo₅ compounds form several orthorhombic hydrides which are structurally closely related. A neutron-diffraction study of β^I, β^II and β^III types, as found for e.g. PrCo₅D_3·6, PrCo₅D_2·9 and CeCo₅D_2·55 respectively, revealed that the deuterium atoms occupy both octahedral and tetrahedral interstices. In the simplest of these, β^I, the occupancy of the interstices is equal; its space group is Cmmm. In both β^II and β^III the c-axis is doubled compared with β_I. In β^II, space group Im2m, the octahedral positions have a uniformly reduced occupancy, which leads to appreciable ordered shifts of the metal atoms. In β^III (Cccm) half of the octahedral positions are vacant, giving a limiting stoichiometric composition CeCo₅H₃.The magnetizations of the (ferromagnetic) hydrides decrease with increasing hydrogen content. Results of neutron-diffraction analysis are in fair agreement with the magnetization measurements.     

Librons observed in liquid acetonitrile by hyper-rayleigh scattering

Hyper-Rayleigh scattering intensity ratios I(VV)/I(VH) in the range 9-26 are observed for liquid acetonitrile (CH 3CN), inconsistent with localized modes of motion in an isotropic fluid. The observations are consistent with propagating orientational modes (librons) with frequency nu = 2 cm (-1), which scatter 71% of the light.     

Single-crystal neutron-diffraction study of AgI between 23° and 300°C

Least-squares refinements and partial Fourier syntheses at several temperatures indicate that the silver density in the high-temperature α-form consists of a tetrahedrally coordinated equilibrium position ($\text{1}\text{4}\text{0}\text{1}\text{2}$) and a three-coordinated saddle point (0.39 0.39 0). This complex silver distribution may be completely accounted for by higher-order thermal tensors. The final R values range from 0.9 to 2.3%.     

Dielectric study of aqueous solution of acetonitrile

Time domain reflectometry method has been used in the frequency range of 10 MHz to 10 GHz to determine dielectric properties of aqueous solutions of acetonitrile in temperature range of 0°C to 40°C. The calibration method based on the least squares fit method has been used. The excess permittivity, activation energy, Kirkwood correlation factor and activation energy of acetonitrile-water system have also been determined. The dielectric data show that acetonitrile molecules interact such that the dipoles have a tendency to remain antiparallel.     

Experimental and kinetic modeling study of oxidation of acetonitrile

Oxidation of acetonitrile has been studied in a flow reactor in the absence and presence of nitric oxide. The experiments were conducted at atmospheric pressure in the temperature range 1150–1450 K, varying the excess air ratio from slightly fuel-lean to very lean. Oxidation of CH₃CN was slow below 1300 K. Nitric oxide, hydrogen cyanide and nitrous oxide were detected as important products. A detailed chemical kinetic model for oxidation of acetonitrile was developed, based on a critical evaluation of data from literature. The rate coefficients for the reactions of CH₃CN and CH₂CN with O₂ were calculated from ab initio theory. Modeling predictions were in satisfactory agreement with experiments. Calculations were sensitive to thermal dissociation of CH₃CN and to the branching fraction for CH₃CN + OH to CH₂CN + H₂O and HOCN + CH₃, respectively. More work is desirable for these steps, as well as for reactions of CH₂CN and HCCN.     

Structural studies of the monoclinic dihydrogen phosphates: A neutron-diffraction study of paraelectric CsH2PO4

The crystal structure of paraelectric CsH₂PO₄ at room temperature is presented. As suggested by the strong deuteration-dependence of the transition temperature and the distribution of quasielastic scattering, one of the hydrogen bonds is found to be very probably (97.5%) disordered, with H-H=0.48(4)Å. This work is set in the context of the interest now being shown in the group of monoclinic dihydrogen phosphates-deuterated KDP, NaDP, the ferroelectric CsDP and the presumed ferroelectric T1DP (DP denotes H₂PO₄). Recent work on these other compounds is surveyed briefly.     

Intermolecular interactions in acetonitrile in a liquid and in a low-temperature argon matrix

IR spectra of acetonitrile embedded in an argon matrix and in a liquid are recorded. IR spectra of specimens obtained with different concentrations of acetonitrile in argon are analyzed. The spectral region of C≡N vibrations of 2200–2300 cm⁻¹ with bands of monomers and possible associates is investigated. Overlap with the band of a hot transition on the low-frequency side is responsible for the pronounced asymmetry of the band ν(C≡N). To whom correspondence should be addressed. St. Petersburg State Institute of Precision Mechanics and Optics (Technical University), 14, Sablinskaya Str., St. Petersburg, 197101, Russia. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 5, pp. 627–631, September–October, 1999.     

A surface tension study of liquid threads

According to symmetry of liquid threads, definitions of surface tension in axial direction and angular direction are given. The formulas of surface tension in axial direction γ_z and surface tension in angular direction γ_θ are derived. A scheme to calculate Δγ = γ_z − γ_θ is designed. We investigate seven different systems (the numbers of molecules N are 1600, 2240, 2880,3360,4000,4800 and 5280) by molecular dynamics simulations. For liquid threads, Δγ increases with the decreasing radius of dividing surface. It shows that there exists surface tension anisotropy for liquid threads. The results obtained by molecular dynamics simulations support that surface tension is dependent on the dividing surface curvature.     

A neutron diffraction study of liquid chloroform

Neutron diffraction studies of the isotopes of chloroform CD³⁵Cl₃ and CD³⁷Cl₃ in liquid phase were carried out at 20°C and a wavelength of 0·7 Å. The data were corrected for background, absorption, multiple scattering and inelastic effects. The coherent distinct differential cross section was separated into intramolecular and intermolecular contributions. The latter, together with intermolecular contributions from neutron scattering data on chloroform of natural isotopic chlorine composition and from X-ray data, was employed to determine four expansion coefficients of the molecular pair correlation function.     

Auger-electron-ion coincidence study of photon-stimulated ion desorption for condensed acetonitrile

Auger-electron-photoion coincidence (AEPICO) studies of photon-stimulated ion desorption (PSID) for condensed acetonitrile induced by carbon core excitation have been performed to elucidate the desorption mechanism related to the Auger process. We have detected only the H⁺ ion in AEPICO spectra. The total ion yield spectrum divided by the total electron yield shows that the desorption efficiency is largely increased at the resonant excitation to C---H*. We have also measured the Auger electron spectrum and the AEPICO yield spectrum at the C---H* excitation. The AEPICO yield spectrum shows enhancement at 245–250 eV electron energy. This seems to be related to the spectator resonant Auger stimulated ion desorption. That is, H⁺ desorption is enhanced due to a two-hole-one-electron state at which the electron is in an anti-bonding C---H* orbital and the two holes can be in a 1π bonding orbital localized on the ---CH₃ group. We have also measured similar spectra for other resonant excitation (π*_CN, σ*_CC, σ*_CN). The results are discussed in connection with the bonding/anti-bonding character and localized character of the excited state.     

Structural studies of the monoclinic dihydrogen phosphates: II. A neutron-diffraction study of TlH2PO4

A neutron-diffraction study of TlH₂PO₄ at room temperature (RT) is presented as part of an investigation of the group of monoclinic dihydrogen phosphates: NaDP, deuterated-KDP, CsDP, and TlDP (DP denotes H₂PO₄). The structure of TlDP, and the nature of its phase transition at 230 K, are discussed and compared with paraelectric CsDP — with which TlDP is nearly isomorphous at RT.     

The neutron-diffraction system on the thermal column of the VVR-S reactor

This article describes the neutron-diffraction system employed on the thermal column of the VVR-S reactor. The system can be used with liquid metals up to 1600 ° C and at angles from 0 ° to 100 °.