Molecular and ionic sublimation of erbium tribromide

The molecular and ionic composition of vapor over erbium tribromide sublimed from the Knudsen effusion cell and the open surface of a single crystal was studied by high-temperature mass spectrometry. The partial pressures of ErBr₃ and Er₂Br₆ molecules in saturated vapor and the ratio between their sublimation coefficients under free vaporization conditions were determined. The enthalpies and activation energies of sublimation of ErBr₃ crystals in the form of monomers and dimers were calculated. The emission of and Er₂ was recorded in studies of ionic sublimation in both modes. The enthalpies of formation of gas molecules and ions were determined. Original Russian Text ? M.F. Butman, L.S. Kudin, V.B. Motalov, A.S. Kryuchkov, A.E. Grishin, K.W. Kr?mer, 2009, published in Zhurnal Fizicheskoi Khimii, 2009, Vol. 83, No. 1, pp. 152–155.     

The molecular and ionic sublimation of holmium tribromide

The molecular and ionic composition of vapor over holmium tribromide was studied by high-temperature mass spectrometry under the conditions of sublimation from a Knudsen effusion cell and from the open single crystal surface. The partial pressures of HoBr₃ and Ho₂Br₆ in saturated vapor and the ratio between their sublimation coefficients under free vaporization conditions were determined. The intensities of lines in the electron impact mass spectra and their temperature dependences were different under Knudsen and Langmuir conditions, which was evidence of superthermal vibrational-rotational excitation of molecules sublimed from the open surface. The enthalpies and activation energies of sublimation of HoBr₃ crystals as monomers and dimers were calculated. The emission of HoBr ₄ ^? and Ho₂Br ₇ ^? negative ions was observed under both sublimation conditions. Ion-molecular equilibria in the LaBr₃-HoBr₃ system were studied. The enthalpies of formation of the HoBr₃ and Ho₂Br₆ molecules and HoBr ₄ ^? and Ho₂Br ₇ ^? negative ions in the gas phase were calculated.     

Photoelectron studies of adsorption and catalysis on the surface of metal single crystals and polycrystals

The potential of photoelectron spectroscopy (XPS) and its use in studies of the state of the surface and adsorption processes on bulk metal samples (disk single crystals, polycrystalline foil and plates) are discussed. Methods for determining the electronic state of the surface layer and geometrical localization of adsorbed atoms on the metal surface using angle-resolved photoelectron spectroscopy are described. The spectrokinetic use of the dynamic mode of XPS with high accuracy and time resolution for kinetic studies of fast processes on the surface (adsorption-desorption, reconstruction, reaction, diffusion-segregation) is considered in detail.     

Molecular orientation in tetraiodoethylene single crystals

Crystals of C₂I₄ have been grown, and their unit cell, twinning, optics and vibrational spectra examined, using precession camera, polarising microscopy, laser Raman and polarised infrared techniques. Vibrational assignments permitted the calculation of force constants for the molecule. It was deduced that the C-C bond directions are at least partially ordered in the crystal, and lie approximately parallel to a the reciprocal lattice direction.     

Lattice relaxation and electric-field-gradient calculations in impurity-doped single ionic crystals

The lattice-relaxation parameters in several ionic crystals doped with monovalent impurity ions are calculated by energy minimization, taking into account the Coulomb, overlap-repulsive, and three-body potential energies. The displaced 256 ions around one substitutional impurity ion are taken into consideration and the results are utilized to calculate the electric-field gradients at sites similar to the (1,0,0), (1,1,0), and (1,1,1) sites relative to the impurity at (0,0,0), by using two different models for three-body potentials.     

The thermodynamic characteristics of sublimation of fenamate molecular crystals

The temperature dependences of vapor pressure were determined by the transpiration method and the thermodynamic functions of sublimation were calculated for six molecular crystals from the group of nonsteroidal antiinflammatory drugs, for niflumic, flufenamic, tolfenamic, mefenamic, and N-phenylanthranylic acids and diphenylamine. The influence of substituents on the enthalpies of sublimation of compounds of this class was studied. A correlation was observed between the enthalpies of sublimation under standard conditions and the temperatures of fusion.     

Molecular dynamics simulations of shock waves in oriented nitromethane single crystals

The structural relaxation of crystalline nitromethane initially at T = 200 K subjected to moderate (~15 GPa) supported shocks on the (100), (010), and (001) crystal planes has been studied using microcanonical molecular dynamics with the nonreactive Sorescu-Rice-Thompson force field [D. C. Sorescu, B. M. Rice, and D. L. Thompson, J. Phys. Chem. B 104, 8406 (2000)]. The responses to the shocks were determined by monitoring the mass density, the intermolecular, intramolecular, and total temperatures (average kinetic energies), the partitioning of total kinetic energy among Cartesian directions, the radial distribution functions for directions perpendicular to those of shock propagation, the mean-square displacements in directions perpendicular to those of shock propagation, and the time dependence of molecular rotational relaxation as a function of time. The results show that the mechanical response of crystalline nitromethane strongly depends on the orientation of the shock wave. Shocks propagating along [100] and [001] result in translational disordering in some crystal planes but not in others, a phenomenon that we refer to as plane-specific disordering; whereas for [010] the shock-induced stresses are relieved by a complicated structural rearrangement that leads to a paracrystalline structure. The plane-specific translational disordering is more complete by the end of the simulations (~6 ps) for shock propagation along [001] than along [100]. Transient excitation of the intermolecular degrees of freedom occurs in the immediate vicinity of the shock front for all three orientations; the effect is most pronounced for the [010] shock. In all three cases excitation of molecular vibrations occurs more slowly than the intermolecular excitation. The intermolecular and intramolecular temperatures are nearly equal by the end of the simulations, with 400-500 K of net shock heating. Results for two-dimensional mean-square molecular center-of-mass displacements, calculated as a function of time since shock wave passage in planes perpendicular to the direction of shock propagation, show that the molecular translational mobility in the picoseconds following shock wave passage is greatest for [001] and least for the [010] case. In all cases the root-mean-square center-of-mass displacement is small compared to the molecular diameter of nitromethane on the time scale of the simulations. The calculated time scales for the approach to thermal equilibrium are generally consistent with the predictions of a recent theoretical analysis due to Hooper [J. Chem. Phys. 132, 014507 (2010)].     

FTIR and thermal studies on gel grown neodymium tartrate crystals

The growth of neodymium tartrate crystals was achieved in silica gel by single diffusion method. Optimum conditions were established for the growth of good quality crystals. Fourier transform infrared (FT-IR) spectroscopic study indicates the presence of water molecules and tartrate ligands and suggests that tartrate ions are doubly ionised. The thermal behaviour of the material was studied using thermogravimetry (TG), differential thermal analysis (DTA), derivative thermogravimetry (DTG) and differential scanning calorimetry (DSC). Thermogravimetric analysis support the suggested chemical formula of the grown crystal to be Nd₂(C₄H₄O₆)₃·7H₂O, and the presence of seven water molecules as water of hydration. It is shown that the material is thermally stable up 45 °C beyond which it decomposes through many stages till the formation of neodymium oxide (Nd₂O₃) at 995 °C. The decomposition pattern is reported to be typical of a hydrated metal tartrate.     

Colloidal single crystals of silica spheres in the presence of simple- and poly-electrolytes,and ionic detergents

Colloidal single crystals of silica spheres (103 nm in diameter) are formed in the presence of various kinds of salts 1 simple electrolytes, i.e., sodium chloride, calcium chloride and lanthanum chloride, 2 polyelectrolytes such as 3–6 type ionen polymer (polybrene), poly-N-ethylpyridinium bromide, a copolymer ofN-benzyl pyridinium chloride andN-hexadecyl pyridinium bromide, and sodium polyethylene sulfonate, and 3 cationic and anionic detergents, hexadecyltrimethylammonium bromide and sodium dodecylsulfate. Shape and size of their single crystals, phase diagram, and the relationship between the two parameters among the critical concentration of melting, conductance and pH of the crystal-like suspensions have been studied. Colloidal single crystals ofpositively charged spheres have been formed in this study by the method of the charge reversal of spheres through the strong adsorption of cationic polyelectrolytes onto the anionic silica spheres.     

Methods for calculating the enthalpies of sublimation of organic molecular crystals

Four methods for calculating the enthalpies of sublimation of organic molecular crystals based on different methodological approaches are proposed. Comparative analysis of these methods was carried out and their good predictive ability with respect to various classes of compounds (aliphatic nitro compounds, acyclic and cyclic amines, amides and amino acids, benzene derivatives, heterocyclic compounds,etc.) was demonstrated.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No, 12, pp. 2872–2881, December, 1996.     

Radiation resistance of ionic and ionic-molecular crystals

The factors that determine the stability of ionic and ionic-molecular crystals in ionizing radiation fields are analyzed. The concepts of the fundamental reactivity (stability) of a solid (the ability of the ideal crystal lattice of the material, in which only intrinsic point defects—interstitial ions and vacancies—are present, to undergo radiation-chemical degradation) and the structure-sensitive reactivity determined by the presence of structural and extrinsic defects are introduced. Data on the radiation resistance of crystalline solids (alkali halides, silver halides, and silver azide) are summarized. It is pointed out that the AgHal crystalline matrix should be resistant toward radiation and alkali halide and AgN₃ crystals should not.     

Complete dispersion analysis of single crystal neodymium gallate

A single crystal of neodymium gallate was investigated by FTIR-spectroscopy in the reststrahlen region between 100–1000 cm⁻¹. The three spectra of the crystal in principal orientations were analyzed by dispersion analysis and the dispersion parameters and the dielectric tensor function were obtained. This allows to properly characterize and quantitatively analyze films of this important substrate material by IR-optical methods.     

Metal-containing ionic liquids and ionic liquid crystals based on imidazolium moiety

Ionic liquids and ionic liquid crystals of imidazolium salts composed of various transition and main group metals have been reviewed. Ionic metal complexes of imidazoles and N-heterocyclic carbenes possess the similar properties were also included. These types of ILs and ILCs have been realized as potential solvents, catalysts, catalyst precursors and reagents for many organic transformations and provide ecofriendly protocols. They have also been found to play key roles in material science. Many of these IL systems are air- and moisture stable and are considered as alternatives for air- and moisture sensitive chloroaluminate-based ILs.     

Interfacial free energies of ionic crystals

Minimum values of the liquid-crystal interfacial free energy have been obtained from data on the maximum supercooling of small droplets of solutions of ionic crystals.     

Molecular surface chemistry by metal single crystals and nanoparticles from vacuum to high pressure

Model systems for studying molecular surface chemistry have evolved from single crystal surfaces at low pressure to colloidal nanoparticles at high pressure. Low pressure surface structure studies of platinum single crystals using molecular beam surface scattering and low energy electron diffraction techniques probe the unique activity of defects, steps and kinks at the surface for dissociation reactions (H-H, C-H, C-C, O=O bonds). High-pressure investigations of platinum single crystals using sum frequency generation vibrational spectroscopy have revealed the presence and the nature of reaction intermediates. High pressure scanning tunneling microscopy of platinum single crystal surfaces showed adsorbate mobility during a catalytic reaction. Nanoparticle systems are used to determine the role of metal-oxide interfaces, site blocking and the role of surface structures in reactive surface chemistry. The size, shape and composition of nanoparticles play important roles in determining reaction activity and selectivity and is covered in this tutorial review.     

Thermodynamics of sublimation,thermophysical and structural aspects of the molecular crystals of fenamates

A method of transfer with an inert carrier gas is used to obtain temperature dependences of pressure vapors. The thermodynamic functions of sublimation processes are calculated for seven molecular crystals that belong to the group of non-steroidal anti-inflammatory drugs: diclofenac, niflumic, flufenamic, tolfenamic, mefenamic, N-phenylanthranilic acids, and diphenylamine. Differential scanning calorimetry is applied to study the melting processes of the selected substances. Single crystal X-ray structural literature data are analyzed, and they are compared with the obtained thermodynamic and thermophysical parameters of sublimation and melting processes. A correlation between the values of the enthalpy of sublimation and the melting temperature under standard conditions is found. The effect of different substituents on the crystal lattice energy of this class of compounds is studied.     

Lorentz factors and surface permittivity of ionic crystals

The explicit analytical expressions and the corresponding numerical scheme are proposed for the calculation of Lorentz factors (LF) in ideal ionic crystals. Formulae for the permittivity tensors and local fields based on the calculated LF are given for a number of crystal types, including such as CsCl, NaCl, CaF₂ and ZnS, where Clausius–Mossotti and the addition rules are valid, and others, like Cu₂O, TiO₂, perovskite, wurtzite where the violation of both rules is common. The equations for the wave-vector-dependent permittivity in infinite crystals and for surface and lone layer permittivity are derived, and sample numerical calculations of the bulk, surface, and single layer permittivity are in a reasonable agreement with the data of measurements if the crystal structure parameters and ions' polarizabilities are used as the input data.     

X-Ray scattering study of ionic colloidal crystals

The scattering study of ionic colloidal crystals by using one- and two-dimensional ultra-small-angle scattering techniques is reviewed with a special reference to dilute dispersions. Because of large lattice constants of colloidal crystals, ultra-small angle regions need to be covered either by long distance optical systems combined with a synchrotron X-ray source or by adopting the Bonse–Hart optics. The crystal structure, lattice constant, and crystal orientation can be precisely determined.