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Results for “atomic photoionization”

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 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1982

Atomic photoionization

After a brief historical review, this work discusses in detail the experimental techniques available for the investigation of photoionization processes, presents results on typical atoms, and examines some of the problems yet unsolved; in general, the discussion is concerned primarily with the photoionization of atoms in the spectral range from ionization threshold to about 100 A. The examination of experimental techniques treats such topics as light sources, monochromators and spectrographs, absorption and photoionization cells, branching-ratio studies, and electron-impact 'photoionization'. Photoionization measurements are discussed with reference to total and partial photoionization cross sections.

Samson, J. A. R.↗
DOE OSTI2023

Attosecond time delay in atomic photoionization: Angular-dependent transition from dipole to quadrupole and spin-flip dynamics

The angular distribution of attosecond Wigner time delay has been investigated including both quadrupole and relativistic effects using the relativistic-random-phase approximation that is based on the Dirac equation and includes significant aspects of many-body correlations. Here the results show a dramatic evolution of the time delay from (essentially nonrelativistic) dipole to quadrupole and spin-flip dynamics as a function of angle, thereby providing a venue for studying these interactions at the attosecond level.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1975

Near-threshold photoionization of xenon metastable atoms

Photoionization from metastable levels of atomic xenon has been studied in the wavelength range from the threshold at 4622 A to 2700 A. Structure in the photoionization signal, due to autoionization, is analyzed to provide term values, lifetimes, and line-shape parameters of the autoionizing states. These parameters, together with the estimated absolute cross sections, are used to derive discrete and continuum oscillator strengths.

Rundel, R. D.↗
NASA NTRS1982

Photoionization research on atomic beams. 2: The photoionization cross section of atomic oxygen

An experiment to determine the absolute value of the photo-ionization cross section of atomic oxygen is described. The atoms are produced in an electrical discharge in oxygen gas with 1% hydrogen added. In order to prevent recombination a crossed beam technique is employed. The ions formed are detected by a time-of-flight mass spectrometer. The concentration of oxygen atoms in the beam is 57%. The measured photoionization cross section of atomic oxygen is compared with theoretical data. The results show the participation of autoionization processes in ionization. The cross section at the autoionizing levels detected is considerably higher than the absorption due to the unperturbed continuum. Except for wavelengths where autoionization occurs, the measured ionization cross section is in fair agreement with theory. This holds up to 550 A whereas for shorter wavelengths the theoretical values are much higher.

Comes, F. J.↗
NASA NTRS1976

Absolute measurement of the photoionization cross section of atomic hydrogen with a shock tube for the extreme ultraviolet

The paper reports an experiment which is part of a program to measure the absolute values of the atomic photoionization cross sections of astrophysically abundant elements, particularly in stars and planetary atmospheres. An aerodynamic pressure-driven shock tube constructed from stainless steel with a quadratic cross section was used to measure the photoionization cross section of H I at 19 wavelength points from 910 to 609 A with experimental uncertainties between 7 and 20%. The shock tube was used to produce fully dissociated hydrogen and neon mixtures for the photoabsorption measurements.

Palenius, H. P.↗
NASA NTRS1978

Absolute cross section for photoionization of atomic oxygen

The absolute cross section for photoionization of atomic oxygen from the 2p4 3P ground state of O(0) to the 2p3 4S ground state of O(+) has been measured at five narrow wavelength intervals between 89.8 and 76.2 nm. The cross section near the 2p3 4S threshold is 4.5 Mb + or - 7%. Recent calculations by Taylor and Burke (1976) and by Pradhan and Saraph (1977) are in reasonable agreement with this work. The dipole-length results of Taylor and Burke (4.1 Mb) are in better agreement with the experiment than their dipole-velocity results (3.2 Mb).

Kohl, J. L.↗
DOE OSTI2024

State-Selective Double Photoionization of Atomic Carbon and Neon

Double photoionization (DPI) allows for a sensitive and direct probe of electron correlation, which governs the structure of all matter. For atoms, much of the work in theory and experiment that informs our fullest understanding of this process has been conducted on helium, and efforts continue to explore many-electron targets with the same level of detail to understand the angular distributions of the ejected electrons in full dimensionality. Expanding on previous results, we consider here the double photoionization of two 2p valence electrons of atomic carbon and neon and explore the possible continuum states that are connected by dipole selection rules to the coupling of the outgoing electrons in 3P, 1D, and 1S initial states of the target atoms. Carbon and neon share these possible symmetries for the coupling of their valence electrons. Results are presented for the energy-sharing single differential cross section (SDCS) and triple differential cross section (TDCS), further elucidating the impact of the initial state symmetry in determining the angular distributions that are impacted by the correlation that drives the DPI process.

Yip, Frank L. (ORCID:000000025409495X)↗
NASA NTRS1960

Photoionization of Atomic Oxygen and Nitrogen

A knowledge of the photoionization cross sections of atomic oxygen and atomic nitrogen from the spectral heads down to the x-ray region is necessary for the interpretaton of the behavior of the ionized layers. In this note we examine the available theoretical and experimental data and obtain sets of recommended values.

Dalgarno, Alexander↗
NASA NTRS1976

Photoionization of atoms and molecules

A literature review on the present state of knowledge in photoionization is presented. Various experimental techniques that have been developed to study photoionization, such as fluorescence and photoelectron spectroscopy, mass spectroscopy, are examined. Various atoms and molecules were chosen to illustrate these techniques, specifically helium and xenon atoms and hydrogen molecules. Specialized photoionization such as in positive and negative ions, excited states, and free radicals is also treated. Absorption cross sections and ionization potentials are also discussed.

Samson, J. A. R.↗
DOE OSTI2024

An Orbital Basis Set for Double Photoionization of Atoms and Molecules

The ab initio theoretical treatment of one-photon double photoionization processes has been limited to atoms and diatomic molecules by the challenges posed by large grid-based representations of the double ionized continuum wave function. To provide a path for extensions to polyatomics, an energy-adapted orbital basis approach is demonstrated that reduces the dimensions of such representations and simultaneously allows larger time steps in time-dependent computational descriptions of double ionization. Additionally, an algorithm that exploits the diagonal nature of the two-electron integrals in the grid basis and dramatically accelerates the transformation between grid and orbital representations is presented. Excellent agreement between the present results and benchmark theoretical calculations is found for H – and Be atoms, as well as the hydrogen molecule, including for the triply differential cross sections that relate the angular distribution and energy sharing of all of the particles in the molecular frame.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
NASA NTRS2002

Interchannel Coupling in the Photoionization of Atoms and Ions in the X-Ray Range

To understand how this interchannel coupling, so important in neutral atoms, applies to positive ions, a research program has been initiated to deal with this question, i.e., a program to quantify the effects of interchannel coupling in ionic photoionization, thereby assessing existing photoionization data bases in the x-ray region. To accomplish this task, we have employed the Relativistic Random-Phase-Approximation (RRPA) methodology which includes significant aspects of electron-electron correlation, including interchannel coupling. The RRPA methodology has been found to produce excellent agreement with experiment for neutral Ne at photon energies in the 1 keV range.

Manson, Steven T.↗
DOE OSTI2023

The Spin-Orbit Interaction: A Small Force with Large Implications

The spin-orbit interaction is quite small compared to electrostatic forces in atoms. Nevertheless, this small interaction can have large consequences. Several examples of the importance of the spin-orbit force in atomic photoionization are presented and explained.

74 ATOMIC AND MOLECULAR PHYSICS↗
NASA NTRS1993

HST imaging of hydrogen-poor ejecta in Abell 30 and Abell 78 - Wind-blown cometary structures

HST Faint Object Camera images of hydrogen-poor gas in the planetary nebulae A30 and A78 have revealed remarkable 'cometary' structures in the O III 5007-A forbidden line. Most of these cometary structures, consisting of compact (0.15-0.5 arcsec) knots with radial tails several arcsec in length, are located in an equatorial plane in both nebulae. In addition, two bright, compact (0.3 arcsec) polar knots are present in A30, one of them forming a bow shock. Corresponding polar features in A78 are more diffuse. The central stars of both nebulae have energetic winds which are most likely responsible for the 'cometary' knot morphology. We interpret this morphology in terms of dense (several thousand electrons per cu cm) H-poor condensations whose outer expanding layers are swept outward by stellar winds. Photoionization modeling indicates that while dense knot cores are mostly heated by atomic photoionization, expanding tenuous gas is heated by photoelectrons ejected from abundant dust grains. Our models predict steep temperature gradients for which there is observational evidence and possible abrupt phase transitions in the expanding gas.

Borkowski, Kazimierz J.↗