arXiv subjects

A. R. Cholach

Publications and source records attributed to A. R. Cholach.

3 recordsLinked to original sources

arXiv2024

Freezing-out of heavy isotopes of Kr

The separation of isotopes of natural Krypton at the gas-liquid and liquid-solid phase interfaces was studied under nonequilibrium conditions using a cryogenic cell and mass spectrometry. Condensate formation during Kr cooling begins at an equilibrium temperature, which corresponds to the partial pressure of the dominant isotope 84Kr, and is accompanied by depletion of the gas phase 84Kr with a separation coefficient of ~0.92 due to the excess of the heat of condensation over the heat of dissolution by 70-100 kJ/mol. The formation of a solid phase near the freezing point is accompanied by depletion of the gas phase by heavy isotopes. The separation coefficients 86Kr, 84Kr, 83Kr, 82Kr and 80Kr are about 1.06, 1.11, 0.86, 0.86 and 0.80, respectively, after the transition of ~30% of the atoms to the solid phase. Pressure-selective condensation can be used to separate components with close boiling points when distillation and temperature-selective condensation methods are ineffective, and freezing out of heavy isotopes can be used to enrich elements with practically important isotopes.

cond-mat.mtrl-sci↗

arXiv2016

Conformity of macroscopic behavior to local properties in the catalytic ammonia synthesis and oscillatory reactions on metal surfaces

Unique catalytic potential of metal surfaces has encouraged a great number of basic and applied studies. The manuscript highlights the general regularities in a field on the grounds of strong interrelation between catalytic, kinetic and thermodynamic behaviour of the reaction system. The trials of the catalytic NH3 synthesis and the oscillatory NO+H2 reaction have revealed that the thermodynamics of the local structure determines the properties and multiplicity of the reaction intermediates enabling the peculiar macroscopic kinetics and specific catalytic activity. Structure and activity of catalytic sites are correlated within a realistic model, where total undercoordination of adjacent surface atoms and enthalpy of local reaction is taken as a descriptor for structure and activity, respectively. The model has specified the resonant catalytic centers for NH3 synthesis on metal surfaces in close agreement with experimental data. The basal planes of noble metals are less active than Fe- and Ru-based catalysts, whereas an extraordinary activity of small Pt, Ir and Rh clusters can be expected. A strong advantage of imperfections compared to perfect areas in the surface wave nucleation is evaluated. Isothermal rate oscillations in open heterogeneous catalytic reaction systems are expected under the multiplicity of reaction intermediates fairly different in activity, providing the steady state and reaction rout multiplicity. Switching between active and inactive kinetic brunches gives rise to the explosive coverage changeover that can be visualized as a traveling wave. A single pattern of oscillations in the NO+H2 reaction includes the key role of intermediate NHad species providing the catalytic removal of strongly bound nitrogen. The driving forces, the feedback, and chemical interactions within the traveling waves are clearly understood.

cond-mat.mtrl-sci↗

arXiv2012

The general traits of inelastic electron scattering by the adsorbed system

Inelastic electron scattering by the adsorbate covered Pt(100) single crystal surface is studied by Disappearance Potential Spectroscopy and density of states (DOS) calculations. Two peculiar channels of elastic electron consumption are highlighted, both related to the substrate core level excitation coupled separately with two particular electron transitions. The first channel affects the adsorbed layer and enables to reveal the valence state structure of the adsorbed species as well as the substrate DOS. The second one includes the multiple plasmon oscillations. The proposed mechanism of electron transitions assumes that one-dimensional DOS at the vacuum level is an additional spot for location of excited electrons, along with vacant DOS at the Fermi level. Observed phenomena are supposed to be a general regularity of electron-solid interaction and a useful tool for fingerprinting the adsorbed layer at molecular level.

cond-mat.mtrl-sci↗