Space charge limited currents in one-dimensional systems. The electron mobility in polydiacetylene crystals

A theory for space charge limited currents in electronically one-dimensional solids is given; it is applied to polydiacetylene single crystals which form electronically one-dimensional high-mobility semiconductors. The theory allows the current to vary as the square of the applied voltage even if the carrier drift velocity is saturated.     

Electrode independent chemoresistive response for cobalt phthalocyanine in the space charge limited conductivity regime

The electrical properties of 50 nm thick metallophthalocyanine films, prepared by organic molecular beam epitaxy (OMBE) on interdigitated electrodes, were studied with DC current-voltage measurements and impedance spectroscopy. The transition from Ohmic behavior at low voltages to space-charge-limited conductivity (SCLC) at higher voltages depends on the metal electrode (Pt, Pd, and Au), but does not correlate with the work function of the electrode. Impedance spectroscopy studies show the coexistence of low- and high-frequency traps in the thin film devices, and the contribution of low-frequency traps associated with Ohmic behavior diminishes at higher bias. Although device resistances are strongly influenced by the electrode material, and vary by a factor of over 300, the relative chemical sensor responses on exposure to dimethyl methylphosphonate (DMMP), methanol, water, or toluene vapors are similar for CoPc on Pt, Pd, and Au electrodes when these devices are operated in the SCLC regime at room temperature. When the devices are operated at voltages where the low-frequency interfacial traps are filled, the sensor response to analyte becomes uniform and reliable regardless of the specific interfacial electrode contact.     

Level set topology of the nuclear charge space and the electronic energy functional

Electronic energy level set topologies in the abstract nuclear charge space Z of molecular systems are defined and analyzed. Two theorems, one on the general convexity of level sets in Z, another on homotopies of boundaries of level sets, induced by nuclear geometry variations in the nuclear configuration space R, are proven. The applications of the two theorems are illustrated by examples of various molecules and ions.     

On the possibility of using rubbers in Arctic conditions

This article is devoted to the specific features of the development of compositions and the use of frost-resistant rubbers. The main operating characteristics frost-resistant rubber and the specificity of their use in the Arctic climate are presented.     

On the possibility of using organic phosphors in thermoluminescence dosimetry

Organic materials in general and polymers in particular have traditionally been considered as to be phosphors and have been ruled out as materials which could be useful in dosimetry of ionizing radiations by thermoluminescence. Some results reported during the past decade suggested possibilities of organic phosphors with good thermoluminescence characteristics. Experiments were undertaken to exploit the various possibilities. The results show that “crystalline polymers” can have adequate thermoluminescence properties to be useful in dosimetry. It is suggested that further studies on thermoluminesence in crystalline polymers and highly drawn fibers of high polymers will prove fruitful.     

Electron microtomography: A new method for studying the spatial structure of catalysts

The spatial arrangement of active component (Pt) particles on the surface of a support (Sibunit globule) has been studied by bright-field electron tomography. A tomographic attachment for a standard specimen holder and tomographic grids have been designed. The tomographic procedure has been refined, and adequate tilt series alignment and tomographic reconstruction algorithms have been chosen. The 3D distribution of the active component in the catalyst grain has been studied: particles hidden in micropores have been directly observed, and the size of the pores connecting internal cavities with the exterior has been estimated.     

Nonempirical studies of the lowest electronic states of the TiF molecule using the self-consistent field method in the full active space

Using the self-consistent field method in the full active space (SCF FAS) and the Gaussian basis we calculate 11 lowest electronic states of the TiF molecule, which has been little studied experimentally. We show that thel ² state lies higher than the ground X⁴ state by no more than 4000 cm^–1.Scientific-Production Association, Institute of Applied Chemistry Leningrad. Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 27, No. 4, pp. 455–458, July–August, 1991. Original article submitted October 12, 1990.     

On the possibility of formation of Ti?Mo heteropolyacids on Ti?Mo catalysts

According to IR spectroscopic studies, a Ti–Mo heteropolyacid is formed on the surface of Ti–Mo catalysts prepared from ammonium paramolybdate and TiO₂.

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- , Ti–Mo TiO₂ Ti–Mo .

     

Evidence of the electronic factor for the highly enantioselective catalytic efficiency of Cinchona-derived phase-transfer catalysts

[structure: see text] The Cinchona alkaloid-derived quaternary ammonium salts containing 2'-N-oxypyridine and 2'-cyanobenzene moieties were prepared and evaluated as phase-transfer catalysts in the enantioselective alkylation of glycine imine ester 1. The N-oxypyridine and cyanobenzene moieties might play an important role to form a rigid conformation by coordinating with H(2)O via hydrogen bonding leading to high enantioselectivity (97 approximately >99% ee), which provides evidence of an electronic factor for the high enantioselective catalytic efficiency in phase-transfer alkylation.     

On possibility of creation of azathiene molecular wires for primitive intramolecular electronic devices

Extended acyclic azathienes with aromatic alpha, -substituents satisfy fundamental requirements to molecular wires for intramolecular electronic devices. They can be synthesized and have a Z,E,Z,E-configuration similar to that of the parent polymer poly(azathiene) (SN)_x (a molecular metal and superconductor) with a planar geometry and -MO delocalized over the whole molecule. A stepwise approach corresponding to Empedocles' evolution theory seems to be reasonable in the design of primitive (e.g., disposable) intramolecular electronic devices based on azathiene molecular wires.Institute of Organic Chemistry, Siberian Branch, Russian Academy of Sciences, Novosibirsk. Translated fromZhurnal Strukturnoi Khimii, Vol. 34, No. 6, pp. 106–113, November–December, 1993.Translated by T. Yudanova     

Computing the superexchange electronic factor of electron transfer theory using a grid‐based numerical method

We report a method for calculating the electronic factor in the superexchange rate equation of electron transfer theory; this method is a basis set independent, grid‐based numerical technique that utilizes fast Fourier transforms (FFTs) and a Lanczos recursion in a pseudospectral framework and is used to treat a three‐dimensional one‐electron model of the electronic factor. We compare eigenvalues calculated from the current method to eigenvalues from the literature for both one‐dimensional (1D) and three‐dimensional (3D) model problems and find that the current method provides excellent accuracy and efficiency. With respect to the superexchange electronic factor, we use model potentials to calculate the tunneling matrix elements with the present method to illustrate how the method can be used to address current issues in superexchange. In particular, we show how this method is useful in evaluating the effect of the bridge potential on the superexchange electronic factor when using repulsive‐core pseudopotentials to represent the bridge. © 2000 John Wiley & Sons, Inc. J Comput Chem 21: 1262–1273, 2000     

A new method for recycling asymmetric catalysts via formation of charge transfer complexes

[reaction: see text]. A new concept for recycling asymmetric bis(oxazoline)-type catalysts is reported. The formation of charge-transfer complexes between the chiral ligand and trinitrofluorenone and their subsequent precipitation and reuse by addition of new substrate solutions is described. The efficiency of this procedure is demonstrated in a Diels-Alder reaction to reach the expected endo product as major isomer (up to 97% de and 94% ee): the catalyst was used up to 12 times without loss of either activity or selectivity.     

On the possibility of using of materials based on adhesive prepregs in Arctic conditions

Analysis of the properties of adhesive prepregs, which were synthesized based on glass fabrics and carbon fillers, and materials made on their basis was performed. It was shown that the composite materials based on prepregs with VSK-14-2m binder surpass composite materials based on prepregs synthesized by the impregnation of fabrics with soluble binders in terms of physical and mechanical properties at–130°C, water resistance, hygroscopicity, and water absorption.     

Characterization of charge neutralization reaction in aqueous solution using the membrane separation method

Colloid titration and streaming current detector are two popular techniques used to determine the charge density of dissolved and colloidally dispersed polyelectrolytes. However, both techniques are based on some assumptions that may not be valid under some circumstances. In this paper, a membrane separation technique developed to determine the charge density and characterize a charge neutralization reaction is described. The technique characterizes the reaction between cationic and anionic charge carriers by measuring the counterions released during reaction or the unreacted small molecule charge carriers. Membranes with selected cutoff pore size were used to separate the species of interest from the bulk of the reaction mixture. Three different charge determination techniques were also compared.     

Advancing beyond charge analysis using the electronic localization function: Chemically intuitive distribution of electrostatic moments

We propose here an evaluation of chemically intuitive distributed electrostatic moments using the topological analysis of the electron localization function (ELF). As this partition of the total charge density provides an accurate representation of the molecular dipole, the distributed electrostatic moments based on the ELF partition (DEMEP) allows computing of local moments located at non atomic centers such as lone pairs, sigma bonds and pi systems. As the local dipole contribution can be decomposed in polarization and charge transfer components, our results indicate that local dipolar polarization of the lone pairs and chemical reactivity are closely related whereas the charge transfer contribution is the key factor driving the local bond dipole. Results on relevant molecules show that local dipole contributions can be used to rationalize inductive polarization effects in alcohols derivatives and typical hydrogen bond interactions. Moreover, bond quadrupole polarization moments being related to a pi character enable to discuss bond multiplicities, and to sort families of molecules according to their bond order. That way, the nature of the C-O bond has been revisited for several typical systems by means of the DEMEP analysis which appears also helpful to discuss aromaticity. Special attention has been given to the carbon monoxide molecule, to the CuCO complex and to a weak intramolecular N|-CO interaction involved in several biological systems. In this latter case, it is confirmed that the bond formation is mainly linked to the CO bond polarization. Transferability tests show that the approach is suitable for the design of advanced force fields.     

Simulation of heterogeneous catalysts and catalytic processes using the density functional method

The review is devoted to the use of high-level quantum-chemical calculations by the density functional method for the simulation of heterogeneous catalytic systems based on transition metals. The following problems are considered: (1) the development of methods for simulating metal particles supported on the surfaces of ionic and covalent oxides; (2) the calculation of the properties of individual transition metal atoms and small clusters adsorbed on the surfaces of MgO, α-Al₂O₃, γ-Al₂O₃, and various modifications of SiO₂ and in the pores of zeolites; (3) the mechanisms of hydrogen activation and acrolein hydrogenation on the metallic and partially oxidized surface of silver; and (4) the mechanism of formation of carbon residues upon the decomposition of methanol on nanosized Pd particles.