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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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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1993

Relativistic effects on the bonding and properties of the hydrides of platinum

The ground state of PtH2 and several low-lying states of PtH(+) and PtH have been studied at the all-electron self-consistent-field level of theory to examine the importance of relativistic effects. The results of calculations based on Dirac-Hartree-Fock theory, nonrelativistic theory, and the spin-free no-pair relativistic approximation of Hess are compared to separate the effects of the spin-free terms and the spin-orbit terms of the Hamiltonian on the relativistic corrections to the molecular properties. Comparison is also made between first-order perturbation theory including the one-electron spin-free terms and the method of Hess to determine the size of effects beyond first order. It is found that the spin-orbit interaction significantly affects the properties and energetics of these molecules because of the participation of the Pt 5d orbitals in the bonding, and that effects beyond first order in perturbation theory are large. Any treatment of Pt compounds will have to include both the spin-free and spin-orbit interactions for an accurate description.

Dyall, Kenneth G.↗
DOE OSTI2026

Comparing the fluorination of Pb+ and Po+: insights into p-block relativistic effects for superheavy elements

It is expected that the chemical properties of the heaviest of the superheavy elements (SHEs, = 113 – 118) do not align with what is suggested by their current positions on the periodic table. Specifically, the onset of significant relativistic effects, including increased spin–orbit splitting of the p-orbitals may lead to enhanced stability of low-oxidation states. Notably, it is predicted that flerovium ( = 114) may exhibit pseudo-noble gas behavior from a electron configuration that acts as an ‘inert pair’. Even though it is expected that the – splitting becomes pronounced toward the end of the p-block’s sixth row, there is currently limited experimental evidence to confirm its extent or impact. Here, the production of gas-phase lead ( = 82) and polonium ( = 84) fluoride cations (PbF and PoF ) were compared to elucidate differences in accessible oxidation states. The PoF and PbF species were produced and identified with the FIONA spectrometer at the Lawrence Berkeley National Laboratory 88-Inch Cylctron Facility. Polonium showed notably different fluorination chemistry than lead, producing PoF and PoF as primary products compared to lead’s PbF and PbF . The distribution of PoF products observed offer insights as to the role of spin–orbit splitting for polonium. Similar studies of superheavy elements would elucidate the accessibility of their low-oxidation states as well as to inform chemical predictions for eighth-row elements not yet discovered.

Pore, Jennifer L [Nuclear Science Division, Lawren↗
NASA NTRS2002

Relativistic Effects Around Black Holes: Smearing Absorption Edges

Broad iron absorption structures have been observed in the X-ray spectra of both AGNs and black hole X-ray binaries (BHXBs). A correctly modeled absorption structure can reveal the physical condition of the source, help to determine the continuum spectra and thus help to estimate other spectral lifes more accurately. The absorption structures are usually thought to be caused by the reflection of X-rays by the accretion disks around the central black holes, and the broadening can be a ttributed to the ionization states of the disk and relativistic effects.

Zhang, X. L.↗
NASA NTRS1986

Relativistic effects in astronomical timing measurements

In this paper the relativistic transformations that are necessary to transform the results of earth-based astronomical timing observations from the terrestrial frame in which the observations are made to the proper frame of the astronomical object being observed are derived. Two coordinate systems are considered, the first being the parametrized post-Newtonian coordinate system and the second being a coordinate system based on the use of temps dynamique barycentrique as a time coordinate. Effects due to propagation of signals through curved spacetime and due to the relativistic gravitational time dilation for the earth are derived in each system. The results are then applied to three modern accurate data types spacecraft ranging, pulsar timing, and VLBI. A new effect is found in the analysis of VLBI data, amounting to a rescaling of VLBI-determined baselines produced by the curvature of space in the neighborhood of the sun.

Hellings, R. W.↗
NASA NTRS1974

Relativistic effects of the rotation of the earth on remote clock synchronization

A treatment is given of relativistic clock synchronization effects due to the rotation of the earth. Unlike other approaches, the point of view of an earth fixed coordinate system is used which offers insight to many problems. An attempt is made to give the reader an intuitive grasp of the subject as well as to provide formulae for his use. Specific applications to global timekeeping, navigation, VLBI, relativistic clock experiments, and satellite clock synchronization are discussed. The question of whether atomic clocks are ideal clocks is also treated.

Reinhardt, V.↗
NASA NTRS1977

Atomic electron energies including relativistic effects and quantum electrodynamic corrections

Atomic electron energies have been calculated relativistically. Hartree-Fock-Slater wave functions served as zeroth-order eigenfunctions to compute the expectation of the total Hamiltonian. A first order correction to the local approximation was thus included. Quantum-electrodynamic corrections were made. For all orbitals in all atoms with 2 less than or equal to Z less than or equal to 106, the following quantities are listed: total energies, electron kinetic energies, electron-nucleus potential energies, electron-electron potential energies consisting of electrostatic and Breit interaction (magnetic and retardation) terms, and vacuum polarization energies. These results will serve for detailed comparison of calculations based on other approaches. The magnitude of quantum electrodynamic corrections is exhibited quantitatively for each state.

Aoyagi, M.↗
DOE OSTI2025

Electron correlation and relativistic effects in the excited states of radium monofluoride

Highly accurate and precise electronic structure calculations of heavy radioactive atoms and their molecules are important for several research areas, including chemical, nuclear, and particle physics. Ab initio quantum chemistry can elucidate structural details in these systems that emerge from the interplay of relativistic and electron correlation effects, but the large number of electrons complicates the calculations, and the scarcity of experiments prevents insightful theory-experiment comparisons. Here we report the spectroscopy of the 14 lowest excited electronic states in the radioactive molecule radium monofluoride (RaF), which is proposed as a sensitive probe for searches of new physics. The observed excitation energies are compared with state-of-the-art relativistic Fock-space coupled cluster calculations, which achieve an agreement of ≥99.64% (within ~12 meV) with experiment for all states. Guided by theory, a firm assignment of the angular momentum and term symbol is made for 10 states and a tentative assignment for 4 states. The role of high-order electron correlation and quantum electrodynamics effects in the excitation energies is studied and found to be important for all states.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
NASA NTRS2014

The Nustar Spectrum of Mrk 335: Extreme Relativistic Effects Within Two Gravitational Radii of the Event Horizon?

We present 3-50 keV NuSTAR observations of the active galactic nuclei Mrk 335 in a very low flux state. The spectrum is dominated by very strong features at the energies of the iron line at 5-7 keV and Compton hump from 10-30 keV. The source is variable during the observation, with the variability concentrated at low energies, which suggesting either a relativistic reflection or a variable absorption scenario. In this work, we focus on the reflection interpretation, making use of new relativistic reflection models that self consistently calculate the reflection fraction, relativistic blurring and angle-dependent reflection spectrum for different coronal heights to model the spectra. We find that the spectra can be well fitted with relativistic reflection, and that the lowest flux state spectrum is described by reflection alone, suggesting the effects of extreme light-bending occurring within approx. 2 gravitational radii (RG) of the event horizon. The reflection fraction decreases sharply with increasing flux, consistent with a point source moving up to above 10 RG as the source brightens. We constrain the spin parameter to greater than 0.9 at the 3(sigma) confidence level. By adding a spin-dependent upper limit on the reflection fraction to our models, we demonstrate that this can be a powerful way of constraining the spin parameter, particularly in reflection dominated states. We also calculate a detailed emissivity profile for the iron line, and find that it closely matches theoretical predictions for a compact source within a few RG of the black hole.

galaxies: active aEuro" galaxies: individual: Mrk ↗
DOE OSTI2025

The non-relativistic effective field theory of dark matter-electron interactions

Electronic excitations in atomic, molecular, and crystal targets are at the forefront of the ongoing search for light, sub-GeV dark matter (DM). In many light DM-electron interactions the energy and momentum deposited is much smaller than the electron mass, motivating a non-relativistic (NR) description of the electron. Thus, for any target, light DM-electron phenomenology relies on understanding the interactions between the DM and electron in the NR limit. In this work we derive the NR effective field theory (EFT) of general DM-electron interactions from a top-down perspective, starting from general high-energy DM-electron interaction Lagrangians. This provides an explicit connection between high-energy theories and their low-energy phenomenology in electron excitation based experiments. Furthermore, we derive Feynman rules for the DM-electron NR EFT, allowing observables to be computed diagrammatically, which can systematically explain the presence of in-medium screening effects in general DM models. We use these Feynman rules to compute absorption, scattering, and dark Thomson scattering rates for a wide variety of high-energy DM models.

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS↗
NASA NTRS1986

Prospects for observations of relativistic effects in the solar system

In this paper the authors concentrate on an experiment that promises a dramatic improvement in a classical test of general relativity - the deflection of light by solar gravity. The goal is to measure the post-post-Newtonian contribution of nearly 11 microarcseconds to this deflection. The proposed technique is based on use of an astrometric optical interferometer, POINTS, which could be operated from the bay of the Space Shuttle, mounted on the proposed Space Station, or supported by an independent spacecraft. POINTS should be able to measure the separation of stars about 90 deg apart with an uncertainty of only a few microarcseconds.

Reasenberg, R. D.↗
NASA NTRS2002

The Case for General Relativistic Effects in the Fe K(alpha) Profile of an Active Galaxy

We present results from a simultaneous Chandra HETG (High Energy Transmission Grating) and XMM (X-ray Multi-mirror Mission)-Newton observation of NGC 3516. We find evidence for several narrow components of Fe K(alpha) along with a broad line. We consider the possibility that the lines arise in a blob of material ejected from the nucleus with velocity of approximately 0.25c. We also consider an origin in a neutral accretion disk, suffering enhanced illumination at 35 and 175 R(sub g), perhaps due to magnetic reconnection. The presence of these narrow features indicates there is no Comptonizing region along the line-of-sight to the nucleus. This in turn is compelling support for the hypothesis that broad Fe K(alpha) components are, in general, produced by strong gravity.

Turner, T. J.↗
NASA NTRS1993

Finite nucleus effects on relativistic energy corrections

The effect of using a finite nucleus model in quantum-chemical calculations is examined. Relativistic corrections from the first order Foldy-Wouthuysen terms are affected indirectly by the change in wavefunction, but also directly as a result of revised expressions for the Darwin and spin-orbit terms due to the change in nuclear potential. A calculation for the Rn atom indicates that the mass-velocity and Darwin corrections are much more sensitive to the finite nucleus than the non-relativistic total energy, but that the total contribution for these two terms is quite stable provided the revised form of the Darwin term is used. The spin-orbit interaction is not greatly affected by the choice of nuclear model.

Dyall, Kenneth G.↗