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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 55 records · Page 3
All sourcesNASA NTRSDOE OSTI
NASA NTRS1992

Cross-sections for electron impact ionization of O2

Using a crossed electron beam-molecular beam collision geometry and the relative flow technique measurements have been made to generate a uniform set of electron impact ionization cross-section data for O2 for electron impact energies from threshold to 1000 eV. Present values of total, partial and dissociative ionization cross-sections are compared with previously published data. Cross-sections for the formation of O2(+) from O2 have been measured for the first time.

Krishnakumar, E.↗
DOE OSTI2021

Electron-impact ionization of the Pb atom

Electron-impact ionization cross sections are calculated for the ground configuration of the Pb atom. Time-dependent close-coupling cross sections for the direct ionization of the 6 s and 6 p subshells leading to single ionization are calculated with and without a polarization potential. Configuration-average distorted-wave cross sections for the direct ionization of the 6 s and 6 p subshells leading to single ionization are also calculated with and without a polarization potential. We find the time-dependent close-coupling cross sections using a polarization potential to be in good agreement with convergent-close-coupling cross sections using a polarization potential. The total direct ionization cross sections are compared to two sets of experimental measurements. The differences between the direct ionization cross sections and the experimental measurements are mainly due to indirect ionization cross sections coming from the 6 s 2 6 p 2 → 6 s 6 p 3 excitation followed by autoionization..

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1982

Venus nightside ionosphere - A model with KeV electron impact ionization

The impact of keV electrons is proposed as the strongest source of ionization in a full-up Venus nightside ionosphere model for the equatorial midnight region. The electron impacts lead to a peak ion density of 100,000/cu cm, which was observed by the PV-OIMS experiment on several occasions. In addition, the observed altitude profiles of CO2(+), O(+), O2(+), H(+), and H2(+) can be reproduced by the model on condition that the available keV electron flux is approximated by a reasonable extrapolation from fluxes observed at lower energies.

Kumar, S.↗
DOE OSTI2024

Electron impact ionization in dense plasmas

Here, the distorted-wave with exchange (DWE) method is employed to evaluate electron impact ionization cross sections in dense electron–ion plasmas. Bound and continuum electron wave functions are obtained from a non-relativistic average-atom code. Plots of DWE cross sections are presented for 1s electrons in Li and Be plasmas and 2p electrons in Na and Mg plasmas. For each of these elements, cross sections are evaluated at metallic density in a range of temperatures from 10 to 100 eV and at their respective melting points. Resonances in the cross sections appear near the incident energy threshold at high temperatures. The origin of these resonances is discussed. In general, the distorted wave (DW) method without exchange is found to be a good approximation to the DWE method for electron impact ionization calculations. In the resonance region, however, exchange effects are found to be very important and cannot be neglected.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS2006

Electron-Impact Ionization and Dissociative Ionization of Biomolecules

It is well recognized that secondary electrons play an important role in radiation damage to humans. Particularly important is the damage of DNA by electrons, potentially leading to mutagenesis. Molecular-level study of electron interaction with DNA provides information on the damage pathways and dominant mechanisms. Our study of electron-impact ionization of DNA fragments uses the improved binary-encounter dipole model and covers DNA bases, sugar phosphate backbone, and nucleotides. An additivity principle is observed. For example, the sum of the ionization cross sections of the separate deoxyribose and phosphate fragments is in close agreement with the C3(sup prime)- and C5 (sup prime)-deoxyribose-phospate cross sections, differing by less than 5%. Investigation of tandem double lesion initiated by electron-impact dissociative ionization of guanine, followed by proton reaction with the cytosine in the Watson-Crick pair, is currently being studied to see if tandem double lesion can be initiated by electron impact. Up to now only OH-induced tandem double lesion has been studied.

Huo, Winifred M.↗
NASA NTRS1987

Electron impact ionization in the vicinity of comets

The solar wind interacts very strongly with the extensive cometary coma, and the various interaction processes are initiated by the ionization of cometary neutrals. The main ionization mechanism far outside the cometary bow shock is photoionization by solar extreme ultraviolet radiation.Electron distributions measured in the vicinity of comets Halley and Giacobini-Zinner by instruments on the VEGA and ICE spacecraft, respectively, are used to calculate electron impact ionization frequencies. Ionization by electrons is of comparable importance to photoionization in the magnetosheaths of Comets Halley and Giacobini-Zinner. The ionization frequency in the inner part of the cometary plasma region of comet Halley is several times greater than the photoionization value. Tables of ionization frequencies as functions of electron temperature are presented for H2O, CO2, CO, O, N2, and H.

Cravens, T. E.↗
NASA NTRS1995

Electron impact ionization rates for interstellar neutral H and He atoms near interplanetary shocks: Ulysses observations

During average solar wind flow conditions at 1 AU, ionization rates of interstellar neutrals that penetrate into the inner heliosphere are dominated by charge exchange with solar wind protons for H atoms, and by photoionization for He atoms. During occurrences of strong, coronal mass ejection (CME)-driven interplanetary shock waves near 1 AU, electron impact ionization can make substantial, if not dominating, contributions to interstellar neutral ionization rates in the regions downstream of the shocks. However, electron impact ionization is expected to be relatively less important with increasing heliocentric distance because of the decrease in electron temperature. Ulysses encountered many CME-driven shocks during its journey to and beyond Jupiter, and in addition, encountered a number of strong corotating interaction region (CIR) shocks. These shocks generally occur only beyond approximately 2 AU. Many of the CIR shocks were very strong rivalling the Earth's bow shock in electron heating. We have compared electron impact ionization rates calculated from electron velocity distributions measured downstream from CIR shocks using the Ulysses SWOOPS experiment to charge-exchange rates calculated from measured proton number fluxes and the photoionization rate estimated from an assumed solar photon spectrum typical of solar maximum conditions. We find that, although normally the ratio of electron-impact ionization rates to charge-exchange (for H) and to photoionization (for He) rates amounts to only about one and a few tens of percent, respectively, downstream of some of the stronger CIR shocks they amount to more than 10% and greater than 100%, respectively.

Feldman, W. C.↗
NASA NTRS1995

Electron Impact Ionization and Dissociative Ionization of C2H2

By utilizing a crossed electron beam collision geometry, a combination of time-of-flight (TOF) and quadrupole mass spectrometers, and the relative flow technique1 normalized values of cross sections and appearance energies (AP) were obtained for the formation of singly and multiply ionized species resulting from the ionization and dissociation of C2H2. Details ont he apparatus and technique have been published previously.2,3.

Electron Ionization↗
NASA NTRS1987

Parametrization of electron impact ionization cross sections for CO, CO2, NH3 and SO2

The electron impact ionization and dissociative ionization cross section data of CO, CO2, CH4, NH3, and SO2, measured in the laboratory, were parameterized utilizing an empirical formula based on the Born approximation. For this purpose an chi squared minimization technique was employed which provided an excellent fit to the experimental data.

Srivastava, Santosh K.↗
NASA NTRS1993

Electron impact ionization and attachment cross sections for H2S

Experiments were performed to measure, by electron impact, appearance potentials and the cross sections for ionization, dissociative ionization, and electron attachment for H2S. Results are presented, and discussed individually, for both positive and negative ions. A schematic diagram of the experimental setup is included.

Rao, M. V. V. S.↗