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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 127 records · Page 7
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Vibrationally specific photoionization cross sections of acrolein leading to the Χ{sup ~}A{sup '} ionic state

The vibrational branching ratios in the photoionization of acrolein for ionization leading to the Χ{sup ~}A{sup '} ion state were studied. Computed logarithmic derivatives of the cross section and the corresponding experimental data derived from measured vibrational branching ratios for several normal modes (ν{sub 9}, ν{sub 10}, ν{sub 11}, and ν{sub 12}) were found to be in relatively good agreement, particularly for the lower half of the 11–100 eV photon energy range considered. Two shape resonances have been found near photon energies of 15.5 and 23 eV in the photoionization cross section and have been demonstrated to originate from the partial cross section of the A{sup ′} scattering symmetry. The wave functions computed at the resonance complex energies are delocalized over the whole molecule. By looking at the dependence of the cross section on the different normal mode displacements together with the wave function at the resonant energy, a qualitative explanation is given for the change of the cross sections with respect to changing geometry.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Photoionization cross section measurements of the excited states of cobalt in the near-threshold region

We present measurements of photoionization cross-sections of the excited states of cobalt using a two-color, two-step resonance ionization technique in conjunction with a molecular beam time of flight (TOF) mass spectrometer. The atoms were produced by the laser vaporization of a cobalt rod, coupled with a supersonic gas jet. The absolute photoionization cross-sections at threshold and near-threshold regions (0-1.2 eV) were measured, and the measured values ranged from 4.2±0.7 Mb to 10.5±1.8 Mb. The lifetimes of four odd parity energy levels are reported for the first time.

36 MATERIALS SCIENCE↗
DOE OSTI2014

Communication: Ultrafast time-resolved ion photofragmentation spectroscopy of photoionization-induced proton transfer in phenol-ammonia complex

Photoionization-induced proton transfer (PT) in phenol-ammonia (PhOH-NH{sub 3}) complex has been studied using ultrafast time-resolved ion photofragmentation spectroscopy. Neutral PhOH-NH{sub 3} complexes prepared in a free jet are photoionized by femtosecond [1+1] resonance-enhanced multiphoton ionization via the S{sub 1} state, and the subsequent dynamics occurring in the cations is probed by delayed pulses that result in ion fragmentation. The observed temporal evolutions of the photofragmentation spectra are consistent with an intracomplex PT reaction. The experiments revealed that PT in [PhOH-NH{sub 3}]{sup +} cation proceeds in two distinct steps: an initial impulsive wave-packet motion in ∼70 fs followed by a slower relaxation of about 1 ps that stabilizes the system into the final PT configuration. These results indicate that for a barrierless PT system, even though the initial PT motions are impulsive and ultrafast, the reaction may take a much longer time scale to complete.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Hartree-Fock calculation of the differential photoionization cross sections of small Li clusters

Cross sections and angular distribution parameters for the single-photon ionization of all electron orbitals of Li{sub 2−8} are systematically computed in a broad interval of the photoelectron kinetic energies for the energetically most stable geometry of each cluster. Calculations of the partial photoelectron continuum waves in clusters are carried out by the single center method within the Hartree-Fock approximation. We study photoionization cross sections per one electron and analyze in some details general trends in the photoionization of inner and outer shells with respect to the size and geometry of a cluster. The present differential cross sections computed for Li{sub 2} are in a good agreement with the available theoretical data, whereas those computed for Li{sub 3−8} clusters can be considered as theoretical predictions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Photoionized plasmas induced in neon with extreme ultraviolet and soft X-ray pulses produced using low and high energy laser systems

A comparative study of photoionized plasmas created by two soft X-ray and extreme ultraviolet (SXR/EUV) laser plasma sources with different parameters is presented. The two sources are based on double-stream Xe/He gas-puff targets irradiated with high (500 J/0.3 ns) and low energy (10 J/1 ns) laser pulses. In both cases, the SXR/EUV beam irradiated the gas stream, injected into a vacuum chamber synchronously with the radiation pulse. Irradiation of gases resulted in formation of photoionized plasmas emitting radiation in the SXR/EUV range. The measured Ne plasma radiation spectra are dominated by emission lines corresponding to radiative transitions in singly charged ions. A significant difference concerns origin of the lines: K-shell or L-shell emissions occur in case of the high and low energy irradiating system, respectively. In high energy system, the electron density measurements were also performed by laser interferometry, employing a femtosecond laser system. A maximum electron density for Ne plasma reached the value of 2·10{sup 18 }cm{sup −3}. For the low energy system, a detection limit was too high for the interferometric measurements, thus only an upper estimation for electron density could be made.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2015

Self-sustained criterion with photoionization for positive dc corona plasmas between coaxial cylinders

The positive dc corona plasmas between coaxial cylinders in air under the application of a self-sustained criterion with photoionization are investigated in this paper. A photon absorption function suitable for cylindrical electrode, which can characterize the total photons within the ionization region, is proposed on the basis of the classic corona onset criteria. Based on the general fluid model with the self-sustained criterion, the role of photoionization in the ionization region is clarified. It is found that the surface electric field keeps constant under a relatively low corona current, while it is slightly weakened with the increase of the corona current. Similar tendencies can be found under different conductor radii and relative air densities. The small change of the surface electric field will become more significant for the electron density distribution as well as the ionization activity under a high corona current, compared with the results under the assumption of a constant surface field. The assumption that the surface electric field remains constant should be corrected with the increase of the corona current when the energetic electrons with a distance from the conductor surface are concerned.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2016

Kr photoionized plasma induced by intense extreme ultraviolet pulses

Irradiation of any gas with an intense EUV (extreme ultraviolet) radiation beam can result in creation of photoionized plasmas. The parameters of such plasmas can be significantly different when compared with those of the laser produced plasmas (LPP) or discharge plasmas. In this work, the photoionized plasmas were created in a krypton gas irradiated using an LPP EUV source operating at a 10 Hz repetition rate. The Kr gas was injected into the vacuum chamber synchronously with the EUV radiation pulses. The EUV beam was focused onto a Kr gas stream using an axisymmetrical ellipsoidal collector. The resulting low temperature Kr plasmas emitted electromagnetic radiation in the wide spectral range. The emission spectra were measured either in the EUV or an optical range. The EUV spectrum was dominated by emission lines originating from Kr III and Kr IV ions, and the UV/VIS spectra were composed from Kr II and Kr I lines. The spectral lines recorded in EUV, UV, and VIS ranges were used for the construction of Boltzmann plots to be used for the estimation of the electron temperature. It was shown that for the lowest Kr III and Kr IV levels, the local thermodynamic equilibrium (LTE) conditions were not fulfilled. The electron temperature was thus estimated based on Kr II and Kr I species where the partial LTE conditions could be expected.

70 PLASMA PHYSICS AND FUSION TECHNOLOGY↗
DOE OSTI2019

A Coincidence Velocity Map Imaging Spectrometer for Ions and High-Energy Electrons to Study Inner-Shell Photoionization of Gas-Phase Molecules

We report on the design and performance of a double-sided coincidence velocity map imaging spectrometer optimized for electron-ion and ion-ion coincidence experiments studying inner-shell photoionization of gas-phase molecules with soft X-ray synchrotron radiation. The apparatus employs two microchannel plate detectors equipped with delay-line anodes for coincident, time- and position-resolved detection of photoelectrons and Auger electrons with kinetic energies up to 300 eV on one side of the spectrometer and photoions up to 25 eV per unit charge on the opposite side. We demonstrate its capabilities by measuring valence photoelectrons and ion spectra of neon and nitrogen and by studying channel-resolved photoelectron and Auger spectra along with fragment-ion momentum correlations for chlorine 2 p inner-shell ionization of cis - and trans -1,2-dichloroethene.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2026

Photoabsorption and photoionization of N2 near the first ionization threshold

The photoabsorption and photoionization spectra of molecular nitrogen, N2, near the first ionisation threshold display numerous intense resonances that have not been satisfactorily assigned to date. Principal among these is a pair of broad resonances between 126,200 and 126,600 cm−1 commonly referred to as the ”cathedral” bands. Here, we present new double-resonance photoionization spectra in this region recorded via the 𝑎′′ 1Σ+ 𝑔,𝑣′=0 intermediate state as well as new high-resolution, vacuum-ultraviolet photoabsorption spectra of 14N2,14N15N, and 15N2 to provide additional insight into the assignment of these features. Progress towards a fully consistent interpretation of the existing data on these bands is discussed, and a route towards a comprehensive description of the N2 absorption spectrum up to the 𝐵 2Σ+ 𝑢 state of N+ 2 is proposed.

Nitrogen, vacuum ultraviolet absorption, photoioni↗
DOE OSTI2011

EVIDENCE FOR ULTRA-FAST OUTFLOWS IN RADIO-QUIET ACTIVE GALACTIC NUCLEI. II. DETAILED PHOTOIONIZATION MODELING OF Fe K-SHELL ABSORPTION LINES

X-ray absorption line spectroscopy has recently shown evidence for previously unknown Ultra-fast Outflows (UFOs) in radio-quiet active galactic nuclei (AGNs). These have been detected essentially through blueshifted Fe XXV/XXVI K-shell transitions. In the previous paper of this series we defined UFOs as those highly ionized absorbers with an outflow velocity higher than 10,000 km s{sup -1} and assessed the statistical significance of the associated blueshifted absorption lines in a large sample of 42 local radio-quiet AGNs observed with XMM-Newton. The present paper is an extension of that work. First, we report a detailed curve of growth analysis of the main Fe XXV/XXVI transitions in photoionized plasmas. Then, we estimate an average spectral energy distribution for the sample sources and directly model the Fe K absorbers in the XMM-Newton spectra with the detailed Xstar photoionization code. We confirm that the frequency of sources in the radio-quiet sample showing UFOs is >35% and that the majority of the Fe K absorbers are indeed associated with UFOs. The outflow velocity distribution spans from {approx}10,000 km s{sup -1} ({approx}0.03c) up to {approx}100,000 km s{sup -1} ({approx}0.3c), with a peak and mean value of {approx}42,000 km s{sup -1} ({approx}0.14c). The ionization parameter is very high and in the range log {xi} {approx} 3-6 erg s{sup -1} cm, with a mean value of log {xi} {approx} 4.2 erg s{sup -1} cm. The associated column densities are also large, in the range N{sub H} {approx} 10{sup 22}-10{sup 24} cm{sup -2}, with a mean value of N{sub H} {approx} 10{sup 23} cm{sup -2}. We discuss and estimate how selection effects, such as those related to the limited instrumental sensitivity at energies above 7 keV, may hamper the detection of even higher velocities and higher ionization absorbers. We argue that, overall, these results point to the presence of extremely ionized and possibly almost Compton-thick outflowing material in the innermost regions of AGNs. This also suggests that UFOs may potentially play a significant role in the expected cosmological feedback from AGNs and their study can provide important clues on the connection between accretion disks, winds, and jets.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

PHOTOIONIZATION MODELING OF OXYGEN K ABSORPTION IN THE INTERSTELLAR MEDIUM: THE CHANDRA GRATING SPECTRA OF XTE J1817-330

We present detailed analyses of oxygen K absorption in the interstellar medium (ISM) using four high-resolution Chandra spectra toward the X-ray low-mass binary XTE J1817-330. The 11-25 A broadband is described with a simple absorption model that takes into account the pile-up effect and results in an estimate of the hydrogen column density. The oxygen K-edge region (21-25 A) is fitted with the physical warmabs model, which is based on a photoionization model grid generated with the XSTAR code with the most up-to-date atomic database. This approach allows a benchmark of the atomic data which involves wavelength shifts of both the K lines and photoionization cross sections in order to fit the observed spectra accurately. As a result we obtain a column density of N{sub H} = 1.38 {+-} 0.01 Multiplication-Sign 10{sup 21} cm{sup -2}; an ionization parameter of log {xi} = -2.70 {+-} 0.023; an oxygen abundance of A{sub O}= 0.689{sup +0.015}{sub -0.010}; and ionization fractions of O I/O = 0.911, O II/O = 0.077, and O III/O = 0.012 that are in good agreement with results from previous studies. Since the oxygen abundance in warmabs is given relative to the solar standard of Grevesse and Sauval, a rescaling with the revision by Asplund et al. yields A{sub O}=0.952{sup +0.020}{sub -0.013}, a value close to solar that reinforces the new standard. We identify several atomic absorption lines-K{alpha}, K{beta}, and K{gamma} in O I and O II and K{alpha} in O III, O VI, and O VII-the last two probably residing in the neighborhood of the source rather than in the ISM. This is the first firm detection of oxygen K resonances with principal quantum numbers n > 2 associated with ISM cold absorption.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2013

REVERBERATION AND PHOTOIONIZATION ESTIMATES OF THE BROAD-LINE REGION RADIUS IN LOW-z QUASARS

Black hole mass estimation in quasars, especially at high redshift, involves the use of single-epoch spectra with signal-to-noise ratio and resolution that permit accurate measurement of the width of a broad line assumed to be a reliable virial estimator. Coupled with an estimate of the radius of the broad-line region (BLR) this yields the black hole mass M{sub BH}. The radius of the BLR may be inferred from an extrapolation of the correlation between source luminosity and reverberation-derived r{sub BLR} measures (the so-called Kaspi relation involving about 60 low-z sources). We are exploring a different method for estimating r{sub BLR} directly from inferred physical conditions in the BLR of each source. We report here on a comparison of r{sub BLR} estimates that come from our method and from reverberation mapping. Our ''photoionization'' method employs diagnostic line intensity ratios in the rest-frame range 1400-2000 A (Al III {lambda}1860/Si III] {lambda}1892, C IV {lambda}1549/Al III {lambda}1860) that enable derivation of the product of density and ionization parameter with the BLR distance derived from the definition of the ionization parameter. We find good agreement between our estimates of the density, ionization parameter, and r{sub BLR} and those from reverberation mapping. We suggest empirical corrections to improve the agreement between individual photoionization-derived r{sub BLR} values and those obtained from reverberation mapping. The results in this paper can be exploited to estimate M{sub BH} for large samples of high-z quasars using an appropriate virial broadening estimator. We show that the width of the UV intermediate emission lines are consistent with the width of H{beta}, thereby providing a reliable virial broadening estimator that can be measured in large samples of high-z quasars.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

X-ray and EUV spectroscopy of various astrophysical and laboratory plasmas: Collisional, photoionization and charge-exchange plasmas

Several laboratory facilities were used to benchmark theoretical spectral models that are extensively used by astronomical communities. However, there are still many differences between astrophysical environments and laboratory miniatures that can be archived. Here we setup a spectral analysis system for astrophysical and laboratory plasmas to make a bridge between them, and we investigate the effects from non-thermal electrons and the contributions from a metastable level population on level populations and charge stage distribution for coronal-like, photoionized, and geocoronal plasmas. Test applications to laboratory measurement (i.e., electron beam ion trap plasma) and astrophysical observation (i.e., Comet, Cygnus X-3) are presented. A time evolution of the charge stage and level population are also explored for collisional and photoionized plasmas.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2014

SOLAR PHOTOIONIZATION RATES FOR INTERSTELLAR NEUTRALS IN THE INNER HELIOSPHERE: H, He, O, AND Ne

Extreme UV (EUV) spectra from the Thermosphere Ionosphere Mesosphere Energetics and Dynamics (TIMED)/Solar EUV Experiment are used to infer photoionization rates in the inner heliosphere. Relating these rates to various proxies describing the solar EUV radiation, we construct a multi-linear model which allows us to extrapolate ionization rates back to periods when no routine measurements of the solar EUV spectral distribution have been available. Such information is important, e.g., for comparing conditions of the interstellar neutral particles in the inner heliosphere at the time of Ulysses/GAS observations with conditions during the more recent observations of the Interstellar Boundary Explorer. From a period of 11 yr when detailed spectra from both TIMED and three proxies—Solar and Heliospheric Observatory/CELIAS/SEM-rates, F10.7 radio flux, and Mg II core-to-wing indices—have been available, we conclude that the simple model is able to reproduce the photoionization rates with an uncertainty of typically 5%.

79 ASTRONOMY AND ASTROPHYSICS↗
DOE OSTI2017

Photoionization of tungsten ions: experiment and theory for ${{\rm{W}}}^{4+}$

Experimental and theoretical results are reported for single-photon single ionization of the tungsten ion ${{\rm{W}}}^{4+}$. Absolute cross sections have been measured employing the photon-ion merged-beams setup at the Advanced Light Source in Berkeley. Detailed photon-energy scans were performed at 200 meV bandwidth in the 40–105 eV range. Theoretical results have been obtained from a Dirac-Coulomb R-matrix approach employing basis sets of 730 levels for the photoionization of ${{\rm{W}}}^{4+}$. Calculations were carried out for the $4{f}^{14}5{s}^{2}5{p}^{6}5{d}^{2}{}^{3}{{\rm{F}}}_{J}$, J = 2, ground level and the associated fine-structure levels with J = 3 and 4 for the ${{\rm{W}}}^{4+}$ ions. In addition, cross sections have been calculated for the metastable levels $4{f}^{14}5{s}^{2}5{p}^{6}5{d}^{2}{}^{3}{{\rm{P}}}_{0,1,2},{}_{}{}^{1}{\rm{D}}_{2}^{},{}_{}{}^{1}{\rm{G}}_{4}^{},{}_{}{}^{1}{\rm{S}}_{0}^{}$. In conclusion, a very satisfying agreement of theory and experiment is found for the photoionization cross section of ${{\rm{W}}}^{4+}$ which is remarkable given the complexity of the electronic structure of tungsten ions in low charge states.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Photoionization of the I 4d and valence orbitals of methyl iodide

Here, the photoabsorption and photoionization dynamics of the I 4d and valence orbitals in methyl iodide have been studied both experimentally and theoretically. Synchrotron radiation has been employed to measure the total ion yield in the vicinity of the I 4d ionization thresholds. The observed structure, due to excitations into Rydberg or valence states, has been assigned using transition energies and relative intensities computed with time-dependent density functional theory within the Tamm–Dancoff approximation. Photoelectron spectra, recorded with plane polarized radiation in two polarization geometries, have allowed the effect of autoionization on the valence electron angular distributions to be investigated. The spectra obtained at photon energies of 50.62 and 52.34 eV, coinciding respectively with the I 4d 5/2 → σ* and 4d 3/2 → σ* transitions, reveal, in addition to valence shell photoelectron bands, features not associated with simple photoionization of the parent molecule. High resolution photoelectron spectra of the I 4d main-lines display structure resulting from spin–orbit coupling and molecular field splitting. The binding energies of the five states contributing to the (I 4d) -1 ionization have been determined. The iodine (in CH 3 I) N 45 VV Auger spectrum has been measured and the observed structure has been assigned using the core hole binding energies derived in the present work together with established ionization energies of the doubly charged ion. The experimentally determined Auger electron angular distributions have been discussed in relation to the theoretical angular distribution parameter characterizing the spatial alignment of molecular axes in the (I 4d) -1 state.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2020

Photoionization of superheavy atoms: correlation and relativistic effects

Calculations of the photoionization cross sections of the ground states of the superheavy atoms No (Z=102), Cn (Z=112) and Og (Z=118) have been performed using fully relativistic methodologies. The photoionization cross sections are dominated by interchannel coupling, in all cases, over a broad energy range including both outer and inner shells.

74 ATOMIC AND MOLECULAR PHYSICS↗
DOE OSTI2021

Photoionization of open-shell nitrogen confined in C 60

Here, endofullerene photoionization of open-shell N@C 60 is investigated using a coupled-channel, correlated R-matrix approach with additional modifications for a finite spherical-shell fullerene potential. Particular focus is on the initial-state dependence of the photoionization cross section. Comparisons show significant differences between the 1s 2 2s 2 2p 3 ( 4 S) initial state and the metastable 2 D and 2 P states, as well as strong confinement oscillations.

74 ATOMIC AND MOLECULAR PHYSICS↗