Electron cooling by carbon monoxide in the atmospheres of Mars and Venus

Electron cooling, in which free electrons lose energy to vibrational excitation of gases, has been identified as a significant process in the atmospheres of Mars and Venus for electron impact on CO2. This process does not appear to have been evaluated for CO, although the density of CO exceeds that of CO2 in the upper atmospheres of these planets. In this paper electron cooling rates for CO are calculated and compared with existing rates for CO2. It is found that electron cooling by CO becomes more significant than by CO2 above altitudes of about 300 km on Mars and about 168 km on Venus. The sensitivity of the calculated cooling rates to different measurements of the integral cross sections for electron-impact vibrational excitation of CO is also investigated. PACS Codes: 34.80.Gs, 96.12.JtComment: 10 pages, 10 figure

Ab-initio electron scattering cross-sections and transport in liquid xenon

Ab-initio electron - liquid phase xenon fully differential cross-sections for electrons scattering in liquid xenon are developed from a solution of the Dirac-Fock scattering equations, using a recently developed framework [1] which considers multipole polarizabilities, a non-local treatment of exchange, and screening and coherent scattering effects. A multi-term solution of Boltzmann's equation accounting for the full anisotropic nature of the differential cross-section is used to calculate transport properties of excess electrons in liquid xenon. The results were found to agree to within 25% of the measured mobilities and characteristic energies over the reduced field range of 10^{-4} to 1 Td. The accuracies are comparable to those achieved in the gas phase. A simple model, informed by highly accurate gas-phase cross-sections, is presented to transform highly accurate gas-phase cross-sections to improve the liquid cross-sections, which was found to enhance the accuracy of the transport coefficient calculations.Comment: 26 pages, 9 figures. arXiv admin note: text overlap with arXiv:1503.0037

Recommended Positron Scattering Cross Sections for Atomic Systems

We present a critical analysis of available experimental and theoretical cross section data for positron scattering from atomic systems. From this analysis, we present (where data are available) recommended cross sections for total scattering, positronium formation, inelastic scattering, and direct ionization processes. A complete bibliography of available measurement and theory is also presented.We are grateful for the support of the Australian Research Council (Grant Nos. DP140102854, DP150101521, and DP190100696) and our respective institutions—The University of Malaya, Flinders University, and the Australian National University

Low-energy elastic electron interactions with pyrimidine

We present results of measurements and calculations of elastic electron scattering from pyrimidine in the energy range 3–50 eV. Absolute differential and integral elastic cross sections have been measured using a crossed electron-molecule beam spectrometer and the relative flow technique. The measured cross sections are compared with results of calculations using the well-known Schwinger variational technique and an independent-atom model. Agreement between the measured differential cross sections and the results of the Schwinger calculations is good at lower energies but less satisfactory at higher energies where inelastic channels that should be open are kept closed in the calculations

Inclusion of Electron Interactions by Rate Equations in Chemical Models

The concept of treating subranges of the electron energy spectrum as species in chemical models is investigated. This is intended to facilitate simple modification of chemical models by incorporating the electron interactions as additional rate equations. It is anticipated that this embedding of fine details of the energy dependence of the electron interactions into rate equations will yield an improvement in computational efficiency compared to other methods. It will be applicable in situations where the electron density is low enough that the electron interactions with chemical species are significant compared to electron–electron interactions. A target application is the simulation of electron processes in the D-region of the Earth’s atmosphere, but it is anticipated that the method would be useful in other areas, including enhancement of Monte Carlo simulation of electron–liquid interactions and simulations of chemical reactions and radical generation induced by electrons and positrons in biomolecular systems. The aim here is to investigate the accuracy and practicality of the method. In particular, energy must be conserved, while the number of subranges should be small to reduce computation time and their distribution should be logarithmic in order to represent processes over a wide range of electron energies. The method is applied here to the interaction by inelastic and superelastic collisions of electrons with a gas of molecules with only one excited vibrational level. While this is unphysical, it allows the method to be validated by checking for accuracy, energy conservation, maintenance of equilibrium and evolution of a Maxwellian electron spectrum

Coexistence of 1,3-butadiene conformers in ionisation energies and Dyson orbitals

The minimum-energy structures on the torsional potential-energy surface of 1,3-butadiene have been studied quantum mechanically using a range of models including ab initio Hartree-Fock and second-order Møller-Plesset theories, outer valence Green’s function, and density-functional theory with a hybrid functional and statistical average orbital potential model in order to understand the binding-energy ionization energy spectra and orbital cross sections observed by experiments. The unique full geometry optimization process locates the s-trans-1,3-butadiene as the global minimum structure and the s-gauche-1,3-butadiene as the local minimum structure. The latter possesses the dihedral angle of the central carbon bond of 32.81° in agreement with the range of 30°–41° obtained by other theoretical models. Ionization energies in the outer valence space of the conformer pair have been obtained using Hartree-Fock, outer valence Green’s function, and density-functional statistical average orbital potentials models, respectively. The Hartree-Fock results indicate that electron correlation and orbital relaxation effects become more significant towards the inner shell. The spectroscopic pole strengths calculated in the Green’s function model are in the range of 0.85–0.91, suggesting that the independent particle picture is a good approximation in the present study. The binding energies from the density-functional statisticaly averaged orbital potential model are in good agreement with photoelectron spectroscopy, and the simulated Dyson orbitals in momentum space approximated by the density-functional orbitals using plane-wave impulse approximation agree well with those from experimental electron momentum spectroscopy. The coexistence of the conformer pair under the experimental conditions is supported by the approximated experimental binding-energy spectra due to the split conformer orbital energies, as well as the orbital momentum distributions of the mixed conformer pair observed in the orbital cross sections of electron momentum spectroscopy

Electron scattering from pyrazine: elastic differential and integral cross-sections

We report on new measurements for elastic electron scattering from pyrazine. Absolute differential cross sections (DCSs) at seven discrete energies in the range 3–50 eV, and over the scattered electron angular range 10°–129°, were determined using a crossed electron-molecular beam spectrometer in conjunction with the well-established relative flow technique. Integral elastic cross sections were subsequently derived from those DCS data at each energy. Where possible comparison between the present results and those from sophisticated Schwinger multichannel and R-matrix computations is made, with generally quite good quantitative accord being found. Finally, in order to better study some of the rich resonance structure predicted by theory, results from elastic electron excitation functions are presented

Ab initio molecular-replacement phasing for symmetric helical membrane proteins

An ab initio molecular-replacement method for phasing X-ray diffraction data for symmetric helical membrane proteins has been developed. The described method is based on generating all possible orientations of idealized transmembrane helices and using each model in a molecular-replacement search