Showing papers on "Chemical binding published in 1973"

The Force Concept in Chemistry

Abstract: The applications, most of which have been developed in the last decade, of the Hellmann-Feynman (H-F) theorem in molecular quantum mechanics are reviewed. In general, the forces (on the nuclei of molecules) calculated with the use of this theorem provide great qualitative insight into the nature of the phenomena investigated; outstanding examples of these are in the concepts of chemical binding and molecular shapes. However, there are serious limitations in quantitative applications of the H-F theorem with approximate wave functions, since the calculated forces are extremely sensitive to small inaccuracies in the wave functions, especially near the nuclei of interest. Nevertheless, in view of the fact that it is difficult to discern general qualitative features in very accurate or ab initio molecular calculations, the H-F theorem is likely to be a highly useful tool for developing much needed qualitative chemical models which will be based on firm quantum mechanical foundations and will also remain open to quantitative extension, at least in principle.

Inelastic-Electron-Tunneling Spectroscopy of Metal-Insulator-Metal Junctions

Abstract: The inelastic tunneling of electrons in a metal-insulator-metal junction has been shown to be a spectroscopic method for studying the vibrational modes of the whole system. In the present paper we consider the possibility of deducing precise information from this spectroscopy. The low-voltage part of the spectrum (i.e., the $\frac{{d}^{2}I}{d{V}^{2}}\ensuremath{-}\mathrm{v}\mathrm{s}\ensuremath{-}V$ characteristic) gives information about the phonons of the electrodes. The phonon density, which is deduced for a Mg electrode, is critically compared with the density deduced from neutron scattering. The range of this phonon probe is then studied by tunneling into multilayer electrodes. The 40-90-meV range of the characteristic of a Mg-Pb junction exhibits a specific structure due to the lattice vibrations of the insulator. This structure is compared with the infrared spectrum and the phonon density of states of MgO, as well as with a theoretical calculation of the tunneling current in the transfer-Hamiltonian formalism. From the fit obtained, it is deduced that the 30-\AA{}-thick insulator, grown on Mg, is an oxide, in contrast with the insulator grown on Al, which was previously deduced to be a hydroxide. At higher energies (100-500 meV), the vibrational spectrum of molecules contained in the insulator region is observed. The identification of the lines is shown to be accurate and it gives precise information on these molecules, especially about their chemical binding with the insulator. This last point could be important in the future for studying the problem of adsorption on solid surfaces.

Interaction of pesticide-derived chloroaniline residues with soil organic matter1

Abstract: Herbicide-derived chloroaniline residues are immobilized by physical absorption to both the organic and the inorganic fraction of the soil and, in addition, by chemical binding to the soil organic matter. In contrast to the polymerization reactions, the binding of the chloroanilines is strictly a physicochemical process; microbial activity is involved only in the liberation of the chloroanilines from the parent herbicides. The chemical attachment of chloroanilines to humic substances occurs by at least two mechanisms, in a hydrolyzable (probably anil and anilinoquinone) and in a nonhydrolyzable (probably heterocyclic rings and ether bonds) manner. In the test soil (Nixon sandy loam) these two types of bonds immobilized roughly equal amounts of chloroanilines. Free radicals have little or no role in these reactions. The binding of chloroanilines to the soil organic matter greatly increases the persistence of these herbicide-derived residues in the environment.

A technique for the determination of chemical binding to soft contact lenses.

Abstract: ABSTRACT A technique for the determination of chemical binding has been developed which provides a convenient tool to investigate the nature of chemical agent‐soft contact lens interaction. Results show benzalkonium chloride binds but thimerosal does not bind to Bausch & Lomb and Warner‐Lambert soft contact lenses.

Stabilizing disturbed areas during highway construction for pollution control

Abstract: EXPERIMENTS ALONG VIRGINIA HIGHWAYS ON VARIOUS SOIL MATERIALS IN ALL MAJOR GEOGRAPHIC REGIONS OF VIRGINIA WERE ESTABLISHED TO FIND: (A) THE BEST MULCHES AND CHEMICAL BINDING AGENTS FOR EROSION CONTROL AND (B) THE MOST SUITABLE SEEDING MIXTURES AND FERTILIZER COMBINATIONS FOR SEEDINGS IN ALL SEASONS OF THE YEAR. STAIR-STEP GRADING, SHALLOWER SLOPES, ROUGHENED SOIL SURFACES, AND INCORPORATING LIME AND FERTILIZER REDUCED EROSION PER SE OR GAVE EROSION CONTROL BY ESTABLISHING A VEGETATIVE COVER QUICKLY. GOOD GRADING PRACTICES WITH MULTI-STEP APPLICATIONS OF SEED AND FERTILIZER IF NEEDED MAKE TOPSOILING UNNECESSARY. ALTERING SEED MIXTURES WITH THE ADDITION OF CERTAIN ANNUAL AND PERENNIAL SPECIES HAS GIVEN MARKED IMPROVEMENTS FOR ESTABLISHING VEGETATIVE COVERS IN VARIOUS SEASONS OF THE YEAR. WEEPING LOVEGRASS AND GERMAN MILLET HAVE SIGNIFICANTLY IMPROVED THE ESTABLISHMENT OF VEGETATIVE COVER IN SUMMER SEEDINGS, AND CERAL RYE HAS EXTENDED THE SUCCESSFUL SEEDING DATES IN LATE FALL-EARLY WINTER. SUCH SUCCESS WITH "OFF-SEASON" SEEDINGS HAS MADE IT UNNECESSARY TO DISTURB SOILS A SECOND TIME, THUS AVOIDING ADDITIONAL POTENTIAL EROSION. PERENNIAL SPECIES CAN BE SEEDED WITH THE "TEMPORARY" SPECIES OR IN A SECOND-STEP APPLICATION DURING A FAVORABLE SEEDING SEASON. RESULTS WITH CROWNVETCH IN NEW SEEDINGS OR ON OLD SLOPES WITH SPARSE GRASS VEGETATION HAS BEEN VERY SUCCESSFUL, ESPECIALLY IN NORTHERN AND MOUNTAINOUS REGIONS. THE INTERRELATIONSHIPS OF TOPSOILING, FERTILIZER INCORPORATION, SEEDLING ESTABLISHMENT, AND EROSION CONTROL AS RELATED TO POLLUTION CONTROL ON CONSTRUCTION SITES WAS DISCUSSED. AN INTERPRETIVE SUMMARY OF FINDINGS WITH RECOMMENDATIONS FOR IMPLEMENTATION FOR ESTABLISHING VEGETATION OR CONTROLLING EROSION AT ANY SEASON OF THE YEAR FOR HIGHWAY CONSTRUCTION SITES IS GIVEN. /NTIS/