17 research outputs found
Evolution of electronic and ionic structure of Mg-clusters with the growth cluster size
The optimized structure and electronic properties of neutral and singly
charged magnesium clusters have been investigated using ab initio theoretical
methods based on density-functional theory and systematic post-Hartree-Fock
many-body perturbation theory accounting for all electrons in the system. We
have systematically calculated the optimized geometries of neutral and singly
charged magnesium clusters consisting of up to 21 atoms, electronic shell
closures, binding energies per atom, ionization potentials and the gap between
the highest occupied and the lowest unoccupied molecular orbitals. We have
investigated the transition to the hcp structure and metallic evolution of the
magnesium clusters, as well as the stability of linear chains and rings of
magnesium atoms. The results obtained are compared with the available
experimental data and the results of other theoretical works.Comment: 30 pages, 10 figures, 3 table
Fitting the integrated Spectral Energy Distributions of Galaxies
Fitting the spectral energy distributions (SEDs) of galaxies is an almost
universally used technique that has matured significantly in the last decade.
Model predictions and fitting procedures have improved significantly over this
time, attempting to keep up with the vastly increased volume and quality of
available data. We review here the field of SED fitting, describing the
modelling of ultraviolet to infrared galaxy SEDs, the creation of
multiwavelength data sets, and the methods used to fit model SEDs to observed
galaxy data sets. We touch upon the achievements and challenges in the major
ingredients of SED fitting, with a special emphasis on describing the interplay
between the quality of the available data, the quality of the available models,
and the best fitting technique to use in order to obtain a realistic
measurement as well as realistic uncertainties. We conclude that SED fitting
can be used effectively to derive a range of physical properties of galaxies,
such as redshift, stellar masses, star formation rates, dust masses, and
metallicities, with care taken not to over-interpret the available data. Yet
there still exist many issues such as estimating the age of the oldest stars in
a galaxy, finer details ofdust properties and dust-star geometry, and the
influences of poorly understood, luminous stellar types and phases. The
challenge for the coming years will be to improve both the models and the
observational data sets to resolve these uncertainties. The present review will
be made available on an interactive, moderated web page (sedfitting.org), where
the community can access and change the text. The intention is to expand the
text and keep it up to date over the coming years.Comment: 54 pages, 26 figures, Accepted for publication in Astrophysics &
Space Scienc
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STRUCTURE and ENERGETICS OF SIMPLE CARBENES. CH2, CHF, CHC, CHBr, CF, CCA
Heats of formation and bond energies in group III compounds
We present heats of formation and bond energies for Group-III compounds obtained from calculations of molecular ground-state electronic energies. Data for compounds of the form MX0 are presented, where M = B, Al, Ga, and In, X = H, Cl, and CH3, and n = 1-3. Energies for the B, Al, and Ga compounds are obtained from G2 predictions, while those for the In compounds are obtained from CCSD(T)/CBS calculations ; these are the most accurate calculations for indium-containing compounds published to date. In most cases, the calculated thermochemistry is in good agreement with published values derived from experiments for those species that have well-established heats of formation. Bond energies obtained from the heats of formation follow the expected trend (Cl >> CH3 - H). However, the CH3M-(CH3)2 bond energies obtained for trimethylgallium and trimethylindium are considerably stronger (> 15 kcal mol-1) than currently accepted values
Theoretical Calculation of Vibrations of Adsorbed Species
The chemisorption of oxygen on Lithium, Aluminum, Nickel and Copper surfaces has been investigated using the ab initio Hartree-Fock cluster model. These substrates have the possibility for different bonding in that Li is a simple s metal, Al an s, p and Ni(Cu) an s, p, d metal. In all cases, we have calculated binding energy curves as a function of the oxygen-metal distance. Using these curves, we have derived oxygen-metal normal vibrational frequencies, and the equilibrium bond distance. We have compared the calculated vibrational energy with electron energy loss spectroscopic (EELS) data for Al and find a satisfactory agreement. We discuss O adsorbed on Ni(100) for which coverage dependent loss peaks have been reported but no generally acceptable interpretation exists to date.
The Escape Probability of Some Ions from Mars and Titan Ionospheres
The Kinetic Energy Release (KER) for various ionic species coming from two-body dissociations reactions, induced by double photoionization of CO 2, C2H2 and N2O neutral precursors of interest in planetary atmospheres, are reported. The KER distributions as a function of the VUV photon energy in the range of 30-65 eV are extracted from the coincidences spectra obtained by using tunable synchrotron radiation and electron-ion-ion coincidences coupled with ion imaging techniques. This experimental method, coupled with a computational analysis of the data based on a Monte Carlo trajectoriy simulation, allows to discuss about the probability for some ionic species to escape the upper atmosphere of Mars and Titan. In fact, the KER measured for H+, C+, CH+, CH , N+, O+ and CO+ fragment ions are ranging between 1.0 and 6.0 eV, and these translational energy contents are large enough to allow these ionic species in participating in the atmospheric escape from Mars and Titan into space. © 2014 Springer International Publishing