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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 271 records · Page 15
All sourcesNASA NTRSDOE OSTI
NASA NTRS2002

Modeling of Switching and Hysteresis in Molecular Transport

The conventional way of modeling current transport in two and three terminal molecular devices could be inadequate for certain cases involving switching and hysteresis. Here we present an alternate approach. Contrary to the regular way where applied bias directly modulates the conducting energy levels of the molecule, our method introduces a nonlinear potential energy surface varying with the applied bias as a control parameter. A time-dynamics is also introduced properly accounting for switching and hysteresis behavior. Although the model is phenomenological at this stage, we believe any detailed model would contain similar descriptions at its core.

Samanta, Manoj P.↗
NASA NTRS2017

Dissociation and Internal Excitation of Molecular Nitrogen Due to N + N2 Collisions Using Direct Molecular Simulation

In this work we present a molecular level study of N2+N collisions, focusing on excitation of internal energy modes and non-equilibrium dissociation. The computation technique used here is the direct molecular simulation (DMS) method and the molecular interactions have been modeled using an ab−initio potential energy surface (PES) developed at NASA's Ames Research Center. We carried out vibrational excitation calculations between 5000K and 30000K and found that the characteristic vibrational excitation time for the N + N2 process was an order of magnitude lower than that predicted by the Millikan and White correlation. It is observed that during vibrational excitation the high energy tail of the vibrational energy distribution gets over populated first and the lower energy levels get populated as the system evolves. It is found that the non-equilibrium dissociation rate coefficients for the N + N2 process are larger than those for the N2 + N2 process. This is attributed to the non-equilibrium vibrational energy distributions for the N + N2 process being less depleted than that for the N2 +N2 process. For an isothermal simulation we find that the probability of dissociation goes as 1/T(sub tr) for molecules with internal energy (epsilon(sub int)) less than approximately 9.9eV, while for molecules with epsilon (sub int) greater than 9.9eV the dissociation probability was weakly dependent on translational temperature of the system. We compared non-equilibrium dissociation rate coefficients and characteristic vibrational excitation times obtained by using the ab-initio PES developed at NASA's Ames Research Center to those obtained by using an ab-initio PES developed at the University of Minnesota. Good agreement was found between the macroscopic properties and molecular level description of the system obtained by using the two PESs.

Grover, Maninder S.↗
NASA NTRS2003

Atomic Data and Spectral Line Intensities for S XI

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for S XI. The configurations included are 2s(sup 2)2psup 2), 2s2p(sup 3), 2p(sup 4), 2s(sup 2)2p3l and 2s(sup 2)2p4l (I = s , p , d) giving rise to 72 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 32, 60, 90, 120, and 150 Ry. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved: The effects of resonances, proton rates, photoexcitation and cascades on level populations have been investigate. The predicted S XI line intensities are compared with EUV and UV observations of the quiet and active Sun.

Landi, E.↗
NASA NTRS2004

Atomic Data and Spectral Line Intensities for Ne III

Electron impact collision strengths, energy levels, oscillator strengths, and spontaneous radiative decay rates are calculated for Ne III. The configurations used are 2s(sup 2)2p(sup 4), 2s2p(sup 5), 2p(sup 6), 2s(sup 2)2p(sup 3)3(sub s), 2s(sup 2)2p(sup 3)3p, and 2s(sup 2)2p(sup 3)3d giving rise to 86 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 5.2, 10, 15, 20 and 25 Ry. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8) - 10(exp 14)/cc at an electron temperature of logTe/K = 5.0, corresponding to maximum abundance of Ne III. Relative spectral line intensities are calculated.

Landi, E.↗
NASA NTRS2004

Atomic Data and Spectral Line Intensities for Ar XII

Electron impact collision strengths; energy levels; oscillator strengths and spontaneous radiative decay rates are calculated for Ar XII. The configurations used are 2s(exp 2)2p(exp 3), 2s2p(exp4), 2p(exp 5), 2s22p23s, 2s(exp 2)2p(exp 2)3p, and 2s(exp 2)2p(exp 2)3d giving rise to 72 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies: 35,70, 105, 140 and 175 Ry. They are complemented by Coulomb-Born limits towards infinite collision energy for forbidden transitions and line strengths for optically allowed transitions. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8)-101(exp 14) cm(exp -3) at an electron temperature of log T(sub e)/K = 6.4, corresponding to maximum abundance of Ar XII. Relative spectral line intensities are calculated.

Eissner, W.↗
NASA NTRS2004

Atomic Data and Spectral Line Intensities for Ar XII

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ar XII. The configurations used are 2s(sup 2)p(sup 3), 2s(sup 2)p(sup 4), 2p(sup 5), 2s(sup 2)2p(sup 2)3s, 2s(sup 2)2p(sup 2)3p, and 2s(sup 2)2p(sup 2)3d giving rise to 72 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies: 35, 70, 105, 140 and 175 Ry. They are complemented by Coulomb-Born limits towards infinite collision energy for forbidden transitions and line strengths for optically allowed transitions. Excitation rate coefficients are calculated as a function of electron temperature by assuming a Maxwellian electron velocity distribution. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8)-10(exp 14)/cm(exp 3) at an electron temperature of log T(sub e)/K = 6.4, corresponding to maximum abundance of AR-XII. Relative spectral line intensities are calculated.

Eissner, W.↗
NASA NTRS2001

Atomic Data and Spectral Line Intensities for Ne III

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ne III. The configurations used are 2s(sup 2) 2p(sup 4),2s2p(sup 5),2s(sup 2) 2p(sup 3)3s, and 2s(sup 2)3p(sup 3)3d giving rise to 57 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 5, 10, 15, 20, and 25 Ry. Excitation rate coefficients are calculated by assuming a Maxwellian electron velocity distribution at an electron temperature of logT,(K)=5.0, corresponding to maximum abundance of Ne III. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities covering the range of 10(exp 8)-10(exp 14) per cubic centimeter. Relative spectral line intensities are calculated. Proton excitation rates between the lowest three levels have been included in the statistical equilibrium equations. The predicted Ne III line intensities are compared with SERTS rocket measurements of a solar active region and of a laboratory EUV light source.

Bhatia, A. K.↗
NASA NTRS2001

Atomic Data and Spectral Line Intensities for Ni XXI

Electron impact collision strengths, energy levels, oscillator strengths and spontaneous radiative decay rates are calculated for Ni XXI. The configurations used are 2s(sup 2)2p(sup 4), 2s2p(sup 5), 2p(sup 6), 2s(sup 2)2p(sup 3)3s, and 2s(sup 2)3p(sup 3)3d giving rise to 58 fine-structure levels in intermediate coupling. Collision strengths are calculated at five incident energies, 85, 170, 255, 340, and 425 Ry. Excitation rate coefficients are calculated by assuming a Maxwellian electron velocity distribution at an electron temperature of log T(sub e)(K)=6.9, corresponding to maximum abundance of Ni XXI. Using the excitation rate coefficients and the radiative transition rates, statistical equilibrium equations for level populations are solved at electron densities 10(exp 8)-10(exp 14) per cubic centimeter. Relative spectral line intensities are calculated. Proton excitation rates between the lowest three levels have been included in the statistical equilibrium equations. The predicted intensity ratios are compared with available observations.

Bhatia, A. K.↗
DOE OSTI2025

Emerging tension between isospin symmetry and nuclear deformation at 𝐴 = 78

Since the nuclear interaction is, to first order, isospin independent, simple relationships can be derived for 𝐸⁢2 strengths across isobaric analog states within an isobaric triplet. At the same time, there is a well-known relationship between the 2 + excitation energy and the 𝐵(𝐸⁢2;2 + → 0 + ) transition strength in deformed even-even nuclei. Here, we highlight a tension between these two trends in the 𝐴 = 78 isobaric triplet. Recent level-energy determinations indicate that the proton-rich member of the triplet, 78 Zr, is strongly deformed while recent lifetime measurements in 78 Sr and 78 Y, as extrapolated into 78 Zr, would imply that 78 Zr is weakly deformed. Furthermore, we explore the implications of this apparent contradiction and explore potential solutions.

59 ≤ A ≤ 89↗
NASA NTRS1975

K-alpha X-rays from cosmic ray oxygen

Equilibrium charge fractions are calculated for subrelativistic cosmic ray oxygen ions in the interstellar medium. These are used to determine the expected flux of K-alpha rays arising from atomic processes for a number of different postulated interstellar oxygen spectra. Relating these results to the diffuse X-ray background measured at the appropriate energy level suggests an observable line feature. If the flux of low energy cosmic ray oxygen is sufficiently large, K-alpha X-ray line emission from these nuclei will comprise a significant fraction of the total diffuse flux at approximately 0.6 keV. A satellite borne detector with a resolution greater than 30 percent could observe this feature if the subrelativistic interstellar cosmic ray oxygen spectrum is as large as certain theoretical estimates expressed in the text.

Pravdo, S. H.↗
NASA NTRS1993

Predissociation linewidths in O2 B3Sigma-sub-u(-) (v = 0,2)

Results are presented of measurements of the rotational and fine-structure level-specific linewidths in v = 0 and v = 2 of the O2 B3Sigma-sub-u(-) state, which were carried out using laser-induced fluorescence techniques applied to Schumann-Runge absorption transitions from vibrationally excited O2 X3Sigma-sub-g(-) system. These linewidths represent the first measurements reflecting relative predissociation rates among the B-state levels. The linewidths were found to vary considerably among the various energy levels.

Cosby, P. C.↗
NASA NTRS2000

Consensus Assignments for Water Vapor Lines Not Assigned on the HITRAN Database: 13,200 to 16,500/cm

There are nearly 800 water Vapor-lines in the 13,200-16,500/cm region that do not have rovibrational assignments in the HITRAN database. The positions and intensities in the database were determined by Mandin et al., but assignments could not be determined at that time. Polyansky, et al. have now assigned over 600 of the unassigned lines in the 11,200-16,500/cm region. Schwenke has also given rovibrational assignments to many of these unassigned lines throughout the visible and near-infrared. Both articles changed the assignments of some HITRAN lines. Carleer et al. extend assignments to some weaker lines measured by them on new spectra with excellent signal/noise. However, some lines measured by Mandin et al. were omitted by Carleer, et al. because of blends due to lower spectral resolution. The rovibrational assignments of Polyansky et al. completely agree with those in Schwenke's article for only about 200 lines. However, Schwenke's ab initio line list is available on his internet site (http://ccf.arc.nasa.gov/-dschwenke). A detailed comparison of the Polyansky et al.line list, the Carleer et al.line list, and Schwenke's ab initio line list shows a larger number of agreements. In many cases the disagreement is only about the vibrational and/or rotational upper level, while there is agreement on the lower state assignment and energy level, "E", which is of primary importance for atmospheric applications. We will present a line list of "consensus" assignments in the 13,200-16,500/cm region for consideration of inclusion on the HITRAN and GEISA databases. This will substantially reduce the number of unassigned lines on the databases in this spectral region.

Giver, Lawerence P.↗
NASA NTRS2020

Exploring the Limits of the Data-Model-Theory Synergy: “Hot” MW Transitions for Rovibrational IR Studies

In order to further improve the accuracy of rovibrational IR line lists generated from the “Best Theory +Reliable High-resolution Experiment” (BTRHE) strategy from 0.01-0.05 cm-1, or 300-1500 MHz, to ~10 MHz, we explore the current limits of the Data-Model-Theory synergy by examining the accuracy and consistency of existing data, then propose that “hot” bands in microwave (MW) spectra is the solution we need for future enhancements. The Ames SO2 J=0-20 rovibrational energy levels computed on the semi-empirically refined Ames-2 potential energy surface (PES) are fit to the Effective Hamiltonian (EH) model regularly used in the experimental infrared (IR) analysis for SO2 isotopologues. In the fitted EH(Ames) model, the rotational constants A/B/C and all 5 quartic centrifugal distortion constants display clear, systematic, and consistent patterns along the vibrational state energy or quanta. Such consistent patterns may facilitate the vibrational assignments for MW hot bands and extract more information from high temperature MW spectra. Some EH(Expt) analyses were carried out with the lowest order Coriolis Coupling term, C1. Their constants should not be directly compared with other EH(Expt) and EH(Ames) results. After excluding them, our  = EH(Ames)- EH(Expt) analyses for 5 isotopologues (626, 636, 646, 628 and 828) indicates some loss of accuracy and consistency starting from vibrational states as low as 22 or 1000 cm-1. Some EH parameters, e.g. K, may have relative deviations as large as 50-100% and totally lose any recognizable patterns. This simply means that current EH(Expt) models do not have the system-wide consistency we need to further refine the EH(Ames) and Ames rovibrational IR line lists. A large part of such defects are probably inherited from the limited precision of experimental line positions, i.e. 1E-3 ~ 1E-4 cm-1, or 3-30 MHz. This is confirmed in a series of truncation tests using the Ames data. Although the EH(Ames) consistency may help identify unreliable rovibrational EH(Expt) parameters, and make reliable predictions for minor isotopologues and unobserved vibrational bands, we believe only the highly accurate “hot” MW transitions can provide real enhancements for EH(Expt) accuracy and consistency. “Hot” MW spectra should play a more significant role in the future synergy of Data, Model, and Theory in the field of rovibrational IR studies.

Xinchuan Huang↗
NASA NTRS1994

The Infrared Spectrum of H2S From 1 to 5 Microns

The absorption spectra of H2S from 2000 to 11,147 cm(exp -1) have been obtained with spectral resolutions of 0.006, 0.012, and 0.021 cm(exp -1) using the Fourier transform spectrometer at Kitt Peak National Observatory. The transitions of 21 bands have been assigned for the first time and 9 others reanalyzed so that accurate energy levels, band origins, and rotational parameters could be determined. The analysis of these data revealed some remarkable features in the energy spectrum, e.g., fourfold clustering of rotational levels belonging to the symmetric and asymmetric components of local mode manifolds at a high degree of stretching excitation. This paper reports fitted vibrational parameters and predicted band origins of H2S-32 up to 12,735 cm(exp -1). It also presents the degenerate rotational constants and upper state energies of (301)-(202) and (311)-(212) at 1 micron as illustrations of clustering in the local mode limit.

Alexander D. Bykov↗
NASA NTRS2003

Atomic Data and Emission Line Intensities for CA VII

In the present work we calculate energy levels, transition probabilities and electron-ion collisional excitation rates for the 3s(sup 2)3p(sup 2), 3s3p(sup 3) and 3s(sup 2)3p3d configurations of the silicon-like ion Ca VII. The total number of intermediate coupling levels considered is 27. Collision strengths are calculated at seven incident electron energies: 8, 10, 15, 20, 30,40 and 60 Ry, using the Distorted Wave approximation and a 5-configuration model. Excitation rate coefficients are calculated by assuming a Maxwellian distribution of velocities and are used to calculate level populations and line emissivities under the assumption of statistical equilibrium. Line intensity ratios are calculated and compared with observed values measured from SERTS and SOHO/CDS spectra. The diagnostic potential of Ca VII is demonstrated, with particular emphasis on the possibility to measure the Ne/Ca relative abundance through simultaneous observations of Ca VII and N VI lines. Ca VII proves to be an excellent tool for the study of the FIP effect in the solar transition region.

Landi, E.↗
NASA NTRS1977

Molecular cluster theory of CO chemisorption on a nickel /100/ surface

Self-consistent Hartree-Fock-Slater molecular cluster models for the chemisorption of carbon monoxide on a (100) transition metal surface are presented. Energy levels and charge distribution for the CO:Ni5 cluster in C sub 4v symmetry are obtained, and the variation of binding energies with height of the CO molecule above the surface of nickel is studied in detail. Comparison is made with experimental binding energy spectra and with the multiple-scattering results of Batra and Bagus. The redistribution in energy of free-atom valence levels is studied by means of local-densities-of-states diagrams.

Ellis, D. E.↗
DOE OSTI2025

Suppressing Polaronic Defect–Photocarrier Interaction in Halide Perovskites by Pre-distorting Its Lattice

In halide perovskites, photocarriers can have strong polaronic interactions with point defects. For iodide-deficient MAPbI 3 , we found that the Fermi level can shift significantly by 0.6–0.7 eV upon light illumination. This energy level shift is accompanied by the formation of deep electron traps. These experimental observations are consistent with the formation of a Pb–Pb dimer when photoexcited electrons are trapped at an iodide vacancy. Interestingly, we found that this polaronic interaction is suppressed when a portion of MA + cations is replaced by smaller Cs + ions. Density functional theory calculations reveal that Cs-doping can reduce the distance between two Pb atoms across an iodide vacancy, even without electron trapping. The predistortion of the lattice induced by cation replacement resembles the Pb–Pb dimer formed by electron trapping at the defect site, which explains the suppression of light-induced effects observed in the experiment. Furthermore, our finding unveils a counterintuitive strategy to enhance the photostability of halide perovskites by preintroducing distortions into its lattice.

14 SOLAR ENERGY↗
NASA NTRS1981

Collisional excitation of electron Landau levels in strong magnetic fields

The cross sections for the excitation and deexcitation of the quantized transverse energy levels of an electron in a magnetic field are calculated for electron-proton and electron-electron collisions in light of the importance of the cross sections for studies of X-ray pulsar emission. First-order matrix elements are calculated using the Dirac theory of the electron, thus taking into account relativistic effects, which are believed to be important in accreting neutron stars. Results for the collisional excitation of ground state electrons by protons are presented which demonstrate the importance of proton recoil and relativistic effects, and it is shown that electron-electron excitations may contribute 10 to 20% of the excitation rate from electron-proton scattering in a Maxwellian plasma. Finally, calculations of the cross section for electron-proton small-angle scattering are presented which lead to relaxation rates for the electron velocity distribution which are modified by the magnetic field, and to a possible increase in the value of the Coulomb logarithm.

Langer, S. H.↗