Scattering of thermal He beams by crossed atomic and molecular beams. II. The He-Ar van der Waals potential

Differential cross sections for He–Ar scattering at room temperature have been measured. The experimental consistency of these measurements with others performed in different laboratories is demonstrated. Despite this consistency, the present van der Waals well depth of 1.78 meV, accurate to 10%, is smaller by 20% to 50% than the experimental values obtained previously. These discrepancies are caused by differences between the assumed mathematical forms or between the assumed dispersion coefficients of the potentials used in the present paper and those of previous studies. Independent investigations have shown that the previous assumptions are inappropriate for providing accurate potentials from fits to experimental differential cross section data for He–Ar. We use two forms free of this inadequacy in the present analysis: a modified version of the Simons–Parr–Finlan–Dunham (SPFD) potential, and a double Morse–van der Waals (M^2SV) type of parameterization. The resulting He–Ar potentials are shown to be equal to with experimental error, throughout the range of interatomic distances to which the scattering data are sensitive. The SPFD or M^2SV potentials are combined with a repulsive potential previously determined exclusively from fits to gas phase bulk properties. The resulting potentials, valid over the extended range of interatomic distances r≳2.4 Å, are able to reproduce all these bulk properties quite well, without adversely affecting the quality of the fits to the DC

Scattering of thermal He beams by crossed atomic and molecular beams. IV. Spherically symmetric intermolecular potentials for He+ CH_4, NH_3, H_2O, SF_6

Differential scattering cross sections are measured for He+CH_4, NH_3, H_2O, and SF_6, using the crossed molecular beams technique. These data, which are sensitive to the van der Waals attractive minima and adjacent regions of the intermolecular potential, are interpreted in terms of central‐field models. No evidence is found for quenching of the observed diffraction oscillations. The interactions of the isoelectronic hydrides CH_4, NH_3, H_2O with He are found to have decreasing van der Waals radii in this sequence, and their attractive wells all have similar depths. However, the He+SF_6 attractive well is found to be anomalously deep, and provides a counter example to the supposition that only the polarizability of the least polarizable of the interacting partners (atoms or molecules) correlates with the van der Waals well depth. Simple combination rules for predicting unlike‐pair potential parameters from the corresponding like‐pair ones are tested and found inadequate

Ferroelectric Materials for Solar Energy Conversion: Photoferroics Revisited

The application of ferroelectric materials (i.e. solids that exhibit spontaneous electric polarisation) in solar cells has a long and controversial history. This includes the first observations of the anomalous photovoltaic effect (APE) and the bulk photovoltaic effect (BPE). The recent successful application of inorganic and hybrid perovskite structured materials (e.g. BiFeO3, CsSnI3, CH3NH3PbI3) in solar cells emphasises that polar semiconductors can be used in conventional photovoltaic architectures. We review developments in this field, with a particular emphasis on the materials known to display the APE/BPE (e.g. ZnS, CdTe, SbSI), and the theoretical explanation. Critical analysis is complemented with first-principles calculation of the underlying electronic structure. In addition to discussing the implications of a ferroelectric absorber layer, and the solid state theory of polarisation (Berry phase analysis), design principles and opportunities for high-efficiency ferroelectric photovoltaics are presented

Electronic chemical potentials of porous metal-organic frameworks

The binding energy of an electron in a material is a fundamental characteristic, which determines a wealth of important chemical and physical properties. For metal-organic frameworks this quantity is hitherto unknown. We present a general approach for determining the vacuum level of porous metal-organic frameworks and apply it to obtain the first ionisation energy for six prototype materials including zeolitic, covalent and ionic frameworks. This approach for valence band alignment can explain observations relating to the electrochemical, optical and electrical properties of porous frameworks

Ultra-thin oxide films for band engineering: design principles and numerical experiments

AbstractThe alignment of band energies between conductive oxides and semiconductors is crucial for the further development of oxide contacting layers in electronic devices. The growth of ultra thin films on the surface of an oxide material can be used to introduce a dipole moment at that surface due to charge differences. The dipole, in turn, alters the electrostatic potential — and hence the band energies — in the substrate oxide. We demonstrate the fundamental limits for the application of thin-films in this context, applying analytical and numerical simulations, that bridge continuum and atomistic. The simulations highlight the different parameters that can affect the band energy shifting potential of a given thin-film layer, taking the examples of MgO and SnO2. In particular we assess the effect of formal charge, layer orientation, layer thickness and surface coverage, with respect to their effect on the electrostatic potential. The results establish some design principles, important for further development and application of thin-films for band energy engineering in transparent conductive oxide materials

Rapid collapse of spin waves in non-uniform phases of the second Landau level

The spin degree of freedom in quantum phases of the second Landau level is probed by resonant light scattering. The long wavelength spin wave, which monitors the degree of spin polarization, is at the Zeeman energy in the fully spin-polarized state at $\nu$=3. At lower filling factors the intensity of the Zeeman mode collapses indicating loss of polarization. A novel continuum of low-lying excitations emerges that dominates near $\nu$=8/3 and $\nu$=5/2. Resonant Rayleigh scattering reveals that quantum fluids for $\nu<3$ break up into robust domain structures. While the state at $\nu$=5/2 is considered to be fully polarized, these results reveal unprecedented roles for spin degrees of freedom.Comment: 4 pages, 5 figure

Robot Cooperation without Explicit Communication by Fuzzy Signatures and Decision Trees

This paper presents a novel action selection method for multi robot task sharing problem. Two autonomous mobile robots try to cooperate for push a box to a goal position. Both robots equipped with object and goal sensing, but do not have explicit communication ability. We explore the use of fuzzy signatures and decision making system to intention guessing and efficient action selection. Virtual reality simulation is used to build and test our proposed algorithm

Exact quantum mechanical reaction probabilities and rate constants for the isotopic collinear H+H2 reactions

Quantum mechanical calculations on three of the collinear H+H2 reactions involving D-substitutions are presented and compared with each other and with previous calculations on the H+H2 reaction itself. The energy at which the reaction probability becomes appreciable is well predicted by the vibrationally adiabatic model. The reaction probabilities at low energies (``tunneling'') are larger than predicted by tunneling through one-dimensional barriers for motion along the reaction coordinate. The deviations of the exact rates from transition state theory with unit transmission coefficient and with transmission coefficients corrected for tunneling and nonclassical reflection are examined. Transition state theory including tunneling is usually very accurate (correct within 20% for rate constants); but the errors are much larger at temperatures below 300°K. Although the main use of the present results is for testing approximate models of reaction, not for comparison with laboratory experiments, it is interesting to note that the isotope effects are in rough agreement with the (noncollinear) experimental ones. The results are used to examine the general validity of treatments of the dynamics which separate effects due to the different modes of motion

SAIDE: a Semi-Automated interface for Hydrogen/Deuterium Exchange Mass Spectrometry

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