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Results for “photodetachment”

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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101 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Experimental investigations of low-energy (4-40 eV) collisions of O-(2P) ions and O(3P) atoms with surfaces

Using a newly-developed, magnetically confined source, low-energy, ground state oxygen negative ions and neutral atoms are generated. The energy range is variable, and atom and neutrals have been generated at energies varying from 2 eV to 40 eV and higher. It was found that the interaction of these low-energy species with a solid magnesium fluoride target leads to optical emissions in the (at least) visible and infrared regions of the spectrum. Researchers describe y details of the photodetachment source, and present spectra of the neutral and ion glows in the wavelength range 250 to 850 nm (for O/-/) and 600 to 850 nm (for O), and discuss the variability of the emissions for incident energies between 4 and 40 eV.

Orient, O. J.↗
NASA NTRS1992

Formation of ions and radicals from icy grains in comets

Two theoretical models for the formation of radicals from ice grains are examined to determine if this can explain the jets in comets. It is shown that the production rates for these radicals by the photolysis of molecules in the icy grains are not high enough to explain the jets. A new mechanism is proposed involving the release of cations and anions in the gas phase as the icy mantle surrounding the grains is evaporated. Solar visible radiation can then form radicals by photodetachment of the electrons from these anions. The production rate of radicals formed in this manner is in accord with the production rates of the observed radicals.

Jackson, William M.↗
NASA NTRS1995

Thermal instability in the inner coma of a comet

The spacecraft and ground based observations of comet Halley inner coma showed a localized ion density depletion region whose origin is not well understood. Although it has been linked to a thermal instability associated with negative ions, the photodetachment lifetime of negative ions (approximately 1 sec) is too short compared to the electron attachment time scale (approximately 100 sec) for this process to have a significant effect. A mechanism for the ion density depletion based on the thermal instability of the cometary plasma due to the excitation of rotational and vibrational levels of water molecules is proposed. The electron energy losses due to these processes peak near 4000 K (0.36 eV) and at temperatures higher than this value a localized cooling leads to further cooling (thermal instability) due to the increased radiation loss. The resulting increase in recombination leads to an ion density depletion and the estimates for this depletion at comet Halley agree with the observations.

Milikh, G. M.↗
NASA NTRS2001

On Interpreting the Photoelectron Spectra of MgO

The (sup 2)Sigma(+) and (sup 2)Pi states of MgO(-) and the (sup 1)Sigma(+), (sup 1)Pi, and (sup 3)Pi states of MgO are studied using the averaged coupled-pair functional (ACPF) approach. The computed spectroscopic constants are in good agreement with the available experimental data. The computed Franck-Condon factors and photodetachment overlaps are compared with experiment.

Bauschlicher, Charles W., Jr.↗
NASA NTRS2006

Electron-He(+) P-wave Elastic Scattering and Photoabsorption in Two-electron Systems

In a previous paper [Bhatia, Phys. Rev. A 69,032714 (2004)], electron-hydrogen P-wave scattering phase shifts were calculated using the optical potential approach based on the Feshbach projection operator formalism. This method is now extended to the singlet and triplet electron-He(+) P-wave scattering in the elastic region. Phase shifts are calculated using Hylleraas-type correlation functions with up to 220 terms. Results are rigorous lower bounds to the exact phase shifts and they are compared to phase shifts obtained from the method of polarized orbitals and close-coupling calculations. The continuum functions calculated here are used to calculate photoabsorption cross sections. Photoionization cross sections of He and photodetachment cross sections of H(-) are calculated in the elastic region, i.e. leaving He(+) and H in their respective ground states, and compared with previous calculations. Radiative attachment rates are also calculated.

Bhatia, A. K.↗
NASA NTRS2008

Uncertainty Analysis of Air Radiation for Lunar Return Shock Layers

By leveraging a new uncertainty markup technique, two risk analysis methods are used to compute the uncertainty of lunar-return shock layer radiation predicted by the High temperature Aerothermodynamic Radiation Algorithm (HARA). The effects of epistemic uncertainty, or uncertainty due to a lack of knowledge, is considered for the following modeling parameters: atomic line oscillator strengths, atomic line Stark broadening widths, atomic photoionization cross sections, negative ion photodetachment cross sections, molecular bands oscillator strengths, and electron impact excitation rates. First, a simplified shock layer problem consisting of two constant-property equilibrium layers is considered. The results of this simplified problem show that the atomic nitrogen oscillator strengths and Stark broadening widths in both the vacuum ultraviolet and infrared spectral regions, along with the negative ion continuum, are the dominant uncertainty contributors. Next, three variable property stagnation-line shock layer cases are analyzed: a typical lunar return case and two Fire II cases. For the near-equilibrium lunar return and Fire 1643-second cases, the resulting uncertainties are very similar to the simplified case. Conversely, the relatively nonequilibrium 1636-second case shows significantly larger influence from electron impact excitation rates of both atoms and molecules. For all cases, the total uncertainty in radiative heat flux to the wall due to epistemic uncertainty in modeling parameters is 30% as opposed to the erroneously-small uncertainty levels (plus or minus 6%) found when treating model parameter uncertainties as aleatory (due to chance) instead of epistemic (due to lack of knowledge).

Kleb, Bil↗
NASA NTRS2015

Photoejection with Excitation in H(-) and Other Systems

Lyman-alpha radiation, 1216 Angstroms , has been seen from the sun and from various astrophysical sources. This radiation arises from the radiative transition from the 2p(sup 2P) state to the 1s(sup 2S) state of the hydrogen atom. The 2P state can be excited from the 1s(sup 2S) state by electron impact. However, it is possible to produce this excited state by photodetachment of the H(-) ion, leaving the H atom in the 2P state. We have calculated cross sections for this process using Hylleraas-type functions for the H− ion and using the exchange approximation for the photoelectron in the final continuum states of angular momenta equal to 0 and 2. The photoabsorption cross sections in H−ions or He atoms leaving the hydrogen atom and helium ion in 2(sup 2S) are also calculated. Similar calculations havebeen carried out for the Li(+), Be2(+), and C4(+) ions.

photoejection↗
DOE OSTI2020

Laser-assisted high-energy proton pulse extraction for feasibility study of co-located muon source at the SNS

Here, we have experimentally demonstrated the first non-intrusive 1-GeV proton beam extraction for the generation of muons with a temporal structure optimized for Muon Spin Relaxation/Rotation/Resonance (μSR) applications. The proton pulses are extracted based on the laser neutralization of 1 GeV hydrogen ion (H - ) beam in the high energy beam transport of the Spallation Neutron Source (SNS) accelerator. The maximum flux of the extracted proton beam based on laser neutralization causes only 0.2% reduction of the total proton beam used for neutron production, a marked difference from the 20% reduction at other co-located muon and neutron facilities, and thus the proposed method will result in negligible impact on the SNS operation. This paper describes the development of a fiber/solid-state hybrid laser system that has high flexibility of pulse structure and output power, initial experiments on laser neutralization of beam and separation of H 0 beam from the existing SNS accelerator beam line, conversion of H 0 to proton at the SNS linac dump, and measurement results of 30 ns/50 kHz proton pulses. This system conclusively demonstrates the feasibility of laser-based proton beam extraction to power a world-leading μSR facility at the SNS.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2021

Photoelectron Spectroscopic and ab Initio Computational Studies of the Anion, HThO –

The synergetic combination of anion photoelectron spectroscopy and high-level relativistic coupled-cluster calculations was employed to study the anion, HThO-. The atomic connectivity of this anion was found to be HThO- and not ThOH-. Vibrational and electronic energy spacings in the HThO- photoelectron spectrum were measured and calculated, with good agreement between them being found. Computations yielded electronic energies and equilibrium structures as well as enabling orbital analyses. The adiabatic electron affinity of HThO was determined to be 1.297 ± 0.035 eV.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

High-Resolution Photoelectron Spectroscopy of NO3 – Vibrationally Excited Along Its ν3 Mode

The nitrate (NO3) radical has long been the subject of both experimental and theoretical studies due to its complex electronic structure resulting from vibronic interactions between its X̃2A2' and B̃2E' states. In particular, the definite assignment of the fundamental of its degenerate stretching vibration (ν3) is still under debate. Here, we report high-resolution photoelectron spectra of vibrationally pre-excited NO3- using the recently developed IR-cryo-SEVI technique. The anions are excited through infrared (IR) excitation near 1350 cm-1, accessing the ν3 and 2ν3(e') vibrational levels with band centers at 1350.5 and ∼2700 cm-1, respectively. The IR-cryo-SEVI spectrum for 2ν3 pre-excitation shows clear evidence for an intense 321 transition. From the position of this feature (30031 cm-1), the electron affinity of NO3 also determined in this work (31680 cm-1), and the IR excitation energy, we obtain a fundamental frequency of 1051 cm-1 for the ν3 fundamental of the NO3 radical. This assignment and other features in the IR-cryo-SEVI spectra are supported by spectral simulations based on a vibronic Köppel-Domcke-Cederbaum Hamiltonian. The simulations also show that nearly all features in the IR-cryo-SEVI spectra arise because of pseudo-Jahn-Teller coupling between the X̃ and B̃ states of NO3. The results and analysis presented here settle a long-standing controversy regarding the ν3 frequency of NO3.

Anions↗