Pictures of molecular orbitals.
Molecular orbital electron charge density pictures, noting representation close to Hartree-Fock calculation method
MOLECULAR ORBIT↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Pyrite oxidation and reduction - Molecular orbital theory considerations
In this paper, molecular orbital theory is used to explain a heterogeneous reaction mechanism for both pyrite oxidation and reduction. The mechanism demonstrates that the oxidation of FeS2 by Fe(3+) may occur as a result of three important criteria: (1) the presence of a suitable oxidant having a vacant orbital (in case of liquid phase) or site (solid phase) to bind to the FeS2 via sulfur; (2) the initial formation of a persulfido (disulfide) bridge between FeS2 and the oxidant, and (3) an electron transfer from a pi(asterisk) orbital in S2(2-) to a pi or pi(asterisk) orbital of the oxidant.
Luther, George W., III↗
Slater screening constants in atomic and molecular orbitals
Slater screening constants in atomic and molecular orbitals
PERTURBATION THEORY↗
Pictures of Molecular Orbitals
Quantum mechanical concepts and charge density of molecular orbitals
MOLECULAR STRUCTURE↗
Molecular-orbital model for metal-sapphire interfacial strength
Self-consistent-field X-Alpha scattered-wave cluster molecular-orbital models have been constructed for transition and noble metals (Fe, Ni, Cu, and Ag) in contact with a sapphire (Al2O3) surface. It is found that a chemical bond is established between the metal d-orbital electrons and the nonbonding 2p-orbital electrons of the oxygen anions on the Al2O3 surface. An increasing number of occupied metal-sapphire antibonding molecular orbitals explains qualitatively the observed decrease of contact shear strength through the series Fe, Ni, Cu, and Ag.
Johnson, K. H.↗
Molecular orbital theory of vanadium in the rutile structure crystals sno2, tio2 and geo2
Vanadium molecular orbital theory in rutile structure crystals
VANADIUM↗
Effect of vacuum processing on outgassing within an orbiting molecular shield
The limiting hydrogen number density in an orbiting molecular shield is highly dependent on the outgassing rates from the materials of construction for the shield, experimental apparatus, and other hardware contained within the shield. Ordinary degassing temperatures used for ultrahigh vacuum studies (less than 450 C) are not sufficient to process metals so that the contribution to the number density within the shield due to outgassing is less than the theoretically attainable level (approximately 200 per cu. cm). Pure aluminum and type 347 stainless steel were studied as candidate shield materials. Measurements of their hydrogen concentration and diffusion coefficients were made, and the effects of high temperature vacuum processing (greater than 600 C) on their resulting outgassing rates was determined. The densities in a molecular shield due to the outgassing from either metal were substantially less ( 0.003) than the density due to the ambient atomic hydrogen flux at an orbital altitude of 500 km.
Outlaw, R. A.↗
Molecular orbitals and inner-electron-shell chemical shifts for sulfur and chlorine oxy- anions.
Chemical effects in X-ray spectra and inner shell photoelectron spectra of sulfur- and chlorine- oxygen anions and molecular orbital method
MOLECULAR ORBIT↗
Molecular orbital predictions of the vibrational frequencies of some molecular ions
The initial detections of IR vibration-rotation bands in polyatomic molecular ions by recent spectroscopic advances were guided by ab initio prediction of vibrational frequencies. The present calculations predict the vibrational frequencies of additional ions which are candidates for laboratory analysis. Neutral molecule vibrational frequencies were computed at three levels of theory and then compared with experimental data; the effect of scaling was also investigated, in order to determine how accurately vibrational frequencies could be predicted. For 92 percent of the frequencies examined, the relatively simple HF/6-31G theory's vibrational frequencies were within 100/cm of experimental values, with a mean absolute error of 49/cm. On this basis, the frequencies of 30 molecular ions (many possessing astrophysical significance) were computed.
Defrees, D. J.↗
Oxygen evolution on a SrFeO3 anode - Mechanistic considerations from molecular orbital theory
Various pathways proposed in the literature for the evolution of O2 in electrochemical oxidations are explored using the atom superposition and electron delocalization molecular orbital (ASED-MO) theory and the cluster models of the SrFeO3 surface as a prototype material. Calculations indicate that oxygen atoms can be easily formed on the (100) surface as well as on the edge cation sites of a SrFeO3 anode by the discharge of OH(-), followed by its deprotonation and electron transfer to the electrode. The O atoms can form O2 on the edge and corner sites, where the Fe(4+) is coordinated to four and three bulk oxygen anions, respectively. The calculations strongly disfavor mechanisms involving coupling of oxygen atoms adsorbed on different cations as well as a mechanism featuring an ozone intermediate.
Mehandru, S. P.↗
A molecular orbital study of a model of the Mg2+ coordination complex of the self splicing reaction of ribosomal RNA
Recent discoveries have established the fact that RNA is capable of acting as an enzyme. In this study two different types of molecular orbital calculations, INDO and ab initio, were used in an attempt to assess the structural/functional role of the Mg2+ hydrated complex in ribozyme reactions. Preliminary studies indicate that the reaction is multistep and that the Mg2+ complex exerts a stabilizing effect on the intermediate or midpoint of the reaction.
Non-NASA Center↗
Ab initio molecular orbital studies of low-energy, metastable isomers of the ubiquitous cyclopropenylidene
The discovery of cyclopropenylidene in space suggests that other C3H2 isomers may be present, and a tentative detection of one such isomer, propargylene (HCCCH), has been reported. Ab initio molecular orbital theory has been used to characterize five low-lying, metastable isomers of cyclopropenylidene. Extended calculations including the electron correlation energy, show that the lowest in energy is singlet propadienylidene, followed by propargylene; the singlet and triplet of the latter are too close in energy to allow an assignment of the ground state; triplet propadienylidene is at a significantly higher energy. Rotational frequencies computed to an expected accuracy of + or - 1 -2 percent do not confirm the tentative detection of propargylene in space, although the discrepancy between theory and the observation is not so great as to unequivocally rule out this possibility.
Defrees, D. J.↗
Sulfur at nickel-alumina interfaces - Molecular orbital theory
Previous studies on Al-Ni alloys containing sulfur as an impurity suggest that, when S is in the interface between a metal and an oxide scale, it weakens the chemical bonding between them. This paper investigates factors responsible for this effect, using a molecular orbital theory to predict sulfur structures and electronic properties on the Ni-Al2O3 interface. It is shown that, in absence of S, the basal plane of Al2O3 will bind strongly through the Al(3+) cation surface to Ni (111). When segregated S impurity is present on the Ni surface, there are too few interfacial AlS bonds to effect good adhesion, leading to an inhibition of the oxide scale adhesion in NiCrAl alloys.
Hong, S. Y.↗
Molecular orbital studies in oxidation: Sulfate formation and metal-metal oxide adhesion
The chemical mechanisms for sulfate formation from sodium chloride and sulfur trioxide, which is a product of jet fuel combustion was determined. Molten sodium sulfate leads to hot corrosion of the protective oxide layers on turbine blades. How yttrium dopants in nidkel-aluminum alloys used in turbine blades reduce the spalling rate of protective alumina films and enhance their adhesion was also determined. Two other fulfate mechanisms were deduced and structure of carbon monoxide on a clean chronium and clean platinum-titanium alloys surfaces was determined. All studies were by use of the atom superposition and electron delocalization molecular orbital (ASED-MO) theory. Seven studies were completed. Their titles and abstracts are given.
Anderson, A. B.↗
Slater screening constants in atomic and molecular orbitals.
Relation between Slater screening constants and interchangeability of atomic orbitals
QUANTUM MECHANICS↗
A low Earth orbit molecular beam space simulation facility
A brief synopsis of the low Earth orbit (LEO) satellite environment is presented including neutral and ionic species. Two ground based atomic and molecular beam instruments are described which are capable of simulating the interaction of spacecraft surfaces with the LEO environment and detecting the results of these interactions. The first detects mass spectrometrically low level fluxes of reactively and nonreactively surface scattered species as a function of scattering angle and velocity while the second ultrahigh velocity (UHV) molecular beam, laser induced fluorescence apparatus is capable of measuring chemiluminescence produced by either gas phase or gas-surface interactions. A number of proposed experiments are described.
Cross, J. B.↗
An orbiting molecular shield vacuum facility - A materials laboratory in space
Certain classes of materials processing experiments require a combination of near zero gravity and ultrahigh vacuum. This combination of environmental requirements can be obtained within a molecular shield vacuum facility deployed from the Space Shuttle Orbiter. To avoid degradation by Orbiter effluents, it is necessary to deploy the facility from the Orbiter's immediate vicinity to a distance of about 100 meters. This may be achieved with an extendable/retractable boom, so that power and other resources are supplied by the Orbiter. Alternatively, the facility may be deployed as a free-flyer satellite and retrieved on a subsequent Orbiter mission. Preliminary results of boom design and dynamics analyses are presented.
Youngblood, J. W.↗
The Space Shuttle Orbiter molecular environment induced by the supplemental flash evaporator system
The water vapor environment of the Space Shuttle Orbiter induced by the supplemental flash evaporator during the on-orbit flight phase has been analyzed based on Space II model predictions and orbital flight measurements. Model data of local density, column density, and return flux are presented. Results of return flux measurements with a mass spectrometer during STS-2 and of direct flux measurements during STS-4 are discussed and compared with model predictions.
Ehlers, H. K. F.↗