Search results for "physical chemistry"

Crystal growth of new charge-transfer salts based on π-conjugated donor molecules

2016

Abstract New charge transfer crystals of π-conjugated, aromatic molecules (phenanthrene and picene) as donors were obtained by physical vapor transport. The melting behavior, optimization of crystal growth and the crystal structure are reported for charge transfer salts with (fluorinated) tetracyanoquinodimethane (TCNQ-Fx, x=0, 2, 4), which was used as acceptor material. The crystal structures were determined by single-crystal X-ray diffraction. Growth conditions for different vapor pressures in closed ampules were applied and the effect of these starting conditions for crystal size and quality is reported. The process of charge transfer was investigated by geometrical analysis of the cryst…

Herbizide, 5. Mitt. Die Aminomethinylierung im System der 1-(Alkylphenyl)-2-pyrazolin-5-one

1985

Orientation of non-spherical protonated water clusters revealed by infrared absorption dichroism

2018

Infrared continuum bands that extend over a broad frequency range are a key spectral signature of protonated water clusters. They are observed for many membrane proteins that contain internal water molecules, but their microscopic mechanism has remained unclear. Here we compute infrared spectra for protonated and unprotonated water chains, discs, and droplets from ab initio molecular dynamics simulations. The continuum bands of the protonated clusters exhibit significant anisotropy for chains and discs, with increased absorption along the direction of maximal cluster extension. We show that the continuum band arises from the nuclei motion near the excess charge, with a long-ranged amplifica…

Enhanced kinetics of hole transfer and electrocatalysis during photocatalytic oxygen evolution by cocatalyst tuning

2016

Understanding photophysical and electrocatalytic processes during photocatalysis in a powder suspension system is crucial for developing efficient solar energy conversion systems. We report a substantial enhancement by a factor of 3 in photocatalytic efficiency for the oxygen evolution reaction (OER) by adding trace amounts (∼0.05 wt %) of noble metals (Rh and Ru) to a 2 wt % cobalt oxide modified Ta3N5 photocatalyst particulate. The optimized system exhibited high quantum efficiencies (QEs) of up to 28 and 8.4% at 500 and 600 nm in 0.1 M Na2S2O8 at pH 14. By isolation of the electrochemical components to generate doped cobalt oxide electrodes, the electrocatalytic activity of cobalt oxide …

First principles calculations of oxygen vacancy formation and migration in mixed conducting Ba0.5Sr0.5Co1−yFeyO3−δ perovskites

2011

Abstract First-principles supercell calculations of oxygen vacancies in the Ba 0.5 Sr 0.5 Co 1− y Fe y O 3− δ (BSCF) perovskites are presented. The density of states is determined for different iron content and oxygen vacancy concentrations, and the characteristic differences for Co and Fe are discussed. We analyze the dependences of the defect (oxygen vacancy) formation and migration energies on the Fe content and compare the calculated properties with those of related LaCoO 3 and LaFeO 3 perovskites.

Interface thermodynamic model for low pressure evaporation

1979

Adsorption of CO and N 2 molecules at the surface of solid water. A grand canonical Monte Carlo study

2020

International audience; The adsorption of carbon monoxide and nitrogen molecules at the surface of four forms of solid water is investigated by means of grand canonical Monte Carlo simulations. The trapping ability of crystalline Ih and low-density amorphous ices, along with clathrate hy-drates of structures I and II, are compared at temperatures relevant for astrophysics. It is shown that, when considering a gas phase that contains mixtures of carbon monoxide and nitrogen, the trapping of carbon monoxide is favored with respect to that of nitrogen at the surface of all solids, irrespective of the temperature. The results of the calculations also indicate that some amounts of molecules can …

Ion conduction in the KcsA potassium channel analyzed with a minimal kinetic model.

2004

We use a model by Nelson to study the current-voltage and conductance-concentration curves of bacterial potassium channel KcsA without assuming rapid ion translocation. Ion association to the channel filter is rate controlling at low concentrations, but dissociation and transport in the filter can limit conduction at high concentration for ions other than ${\mathrm{K}}^{+}$. The absolute values of the effective rate constants are tentative but the relative changes in these constants needed to qualitatively explain the experiments should be of significance.

Archetype Cationic Iridium Complexes and Their Use in Solid-State Light-Emitting Electrochemical Cells

2009

The archetype ionic transition-metal complexes (iTMCs) [Ir(ppy)2(bpy)][PF6] and [Ir(ppy)2(phen)][PF6], where Hppy = 2-phenylpyridine, bpy = 2,2'-bipyridine, and phen = 1,10-phenanthroline, are used as the primary active components in light-emitting electrochemical cells (LECs). Solution and solid-state photophysical properties are reported for both complexes and are interpreted with the help of density functional theory calculations. LEC devices based on these archetype complexes exhibit long turn-on times (70 and 160 h, respectively) and low external quantum efficiencies (~ 2%) when the complex is used as a pure film. The long turn-on times are attributed to the low mobility of the counter…

Impact of point defects on the elastic properties of BaZrO3: Comprehensive insight from experiments and ab initio calculations

2018

Abstract Acceptor doped BaZrO3 is the prototype of proton conducting perovskites which are of strong interest as electrolytes for intermediate temperature fuel cells. Elastic properties of both dry and hydrated Y-doped BaZrO3 (1.5–17 mol% Y) were determined using ultrasound time of flight (TOF) measurements, and complemented by ab initio calculations which allow for an analysis of the different contributions. The experimental and theoretical findings are consistent and reveal a strong decrease of the Young's, shear and bulk moduli upon increasing dopant concentration. This decrease is attributed to a combined effect of (i) macroscopic lattice chemical expansion mainly caused by differing io…