Showing papers on "Photoionization published in 2011"
TL;DR: The determination of photoemission time delays requires taking into account the measurement process, involving the interaction with a probing infrared field, and this contribution can be estimated using a universal formula and is found to account for a substantial fraction of the measured delay.
Abstract: We study photoionization of argon atoms excited by attosecond pulses using an interferometric measurement technique. We measure the difference in time delays between electrons emitted from the 3s(2) and from the 3p(6) shell, at different excitation energies ranging from 32 to 42 eV. The determination of photoemission time delays requires taking into account the measurement process, involving the interaction with a probing infrared field. This contribution can be estimated using a universal formula and is found to account for a substantial fraction of the measured delay.
485 citations
TL;DR: Experiments in which metastable xenon atoms were ionized with intense 7-micrometer laser pulses from a free-electron laser recorded holographic structures that record underlying electron dynamics on a sublaser-cycle time scale, enabling photoelectron spectroscopy with a time resolution higher than the duration of the ionizing pulse.
Abstract: Ionization is the dominant response of atoms and molecules to intense laser fields and is at the basis of several important techniques, such as the generation of attosecond pulses that allow the measurement of electron motion in real time. We present experiments in which metastable xenon atoms were ionized with intense 7-micrometer laser pulses from a free-electron laser. Holographic structures were observed that record underlying electron dynamics on a sublaser-cycle time scale, enabling photoelectron spectroscopy with a time resolution of almost two orders of magnitude higher than the duration of the ionizing pulse.
424 citations
Book•
08 Apr 2011
TL;DR: In this article, the authors introduce Rmatrix Theorie: Potential Scattering, Multichannel Collision Theory, Resonance and Threshold Behaviour, and Multiphoton Processes: Floquet Theory.
Abstract: Part I - Collision Theory.- Potential Scattering.- Multichannel Collision Theory.- Resonances and Threshold Behaviour.- Part II - R-matrix Theory and Applications.- Introduction to R-matrix Theorie: Potential Scattering.- Electron Collisions with Atoms and Ions.- Intermediate Energy Collision.- Positron Collisions with Atoms and Ions.- Photoionization, Photorecombination and Atoms in Fields.- Multiphoton Processes: Floquet Theory.- Multiphoton Processes: Time-Dependent Theory.- Collisions with Molecules.- Electron Interactions in Solids
352 citations
TL;DR: In this article, a detailed curve of growth analysis of the main Fe XXV/XXVI transitions in photoionized plasmas is presented, and 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.
Abstract: 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–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 ~10,000 km s–1 (~0.03c) up to ~100,000 km s–1 (~0.3c), with a peak and mean value of ~42,000 km s–1 (~0.14c). The ionization parameter is very high and in the range log ξ ~ 3-6 erg s–1 cm, with a mean value of log ξ ~ 4.2 erg s–1 cm. The associated column densities are also large, in the range N H ~ 1022-1024 cm–2, with a mean value of N H ~ 1023 cm–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.
248 citations
TL;DR: In this article, the authors measured the photocurrent excitation spectra to investigate the quenching in the garnet solid solutions, and they concluded that the main quench process in the Y3Al2Ga3O12 (Ce:YAGG) was caused by the direct ionization process from the 5d levels to the conduction band.
Abstract: Photocurrent excitation spectra were measured to investigate the quenching in the garnet solid solutions Intense photocurrent excitation bands attributed to the lowest 5d1 and the second lowest 5d2 levels were observed in the Ce-doped Y3Al2Ga3O12 (Ce:YAGG) and Y3Ga5O12 (Ce:YGG) Based on the results of temperature dependence of photoconductivity, the 5d1 and 5d2 levels in the Ce:YAGG are found to be located below and within the conduction band, respectively, while both levels in the Ce:YGG are found to be located within its conduction band located at lower energy levels In addition, the threshold of photoionization from the 4f level of Ce3+ to the conduction band in the Ce:YAGG and Ce:YGG were estimated to be 32, and 28 eV, respectively We conclude that the main quenching process in the Ce:YAGG is caused by the thermally stimulated ionization process with activation energy of 90 meV from the 5d1 to the conduction band, and that in the Ce:YGG is caused by the direct ionization process from the 5d levels to the conduction band
196 citations
TL;DR: In this paper, the evolution of the VUV mass spectra for two distinct organic aerosol types with temperature is observed to differ dramatically, and the authors postulate that this difference arises from diffusivity within the α-pinene + O 3 reaction (αP).
Abstract: . Vacuum Ultraviolet (VUV) photoionization mass spectrometry has been used to measure the evolution of chemical composition for two distinct organic aerosol types as they are passed through a thermodenuder at different temperatures. The two organic aerosol types considered are primary lubricating oil (LO) aerosol and secondary aerosol from the α-pinene + O 3 reaction (αP). The evolution of the VUV mass spectra for the two aerosol types with temperature are observed to differ dramatically. For LO particles, the spectra exhibit distinct changes with temperature in which the lower m/z peaks, corresponding to compounds with higher vapor pressures, disappear more rapidly than the high m/z peaks. In contrast, the αP aerosol spectrum is essentially unchanged by temperature even though the particles experience significant mass loss due to evaporation. The variations in the LO spectra are found to be quantitatively in agreement with expectations from absorptive partitioning theory whereas the αP spectra suggest that the evaporation of αP derived aerosol appears to not be governed by partitioning theory. We postulate that this difference arises from diffusivity within the αP particles being sufficiently slow that they do not exhibit the expected liquid-like behavior and perhaps exist in a glassy state. To reconcile these observations with decades of aerosol growth measurements, which indicate that OA formation is described by equilibrium partitioning, we present a conceptual model wherein the secondary OA is formed and then rapidly converted from an absorbing form to a non-absorbing form. The results suggest that, although OA growth may be describable by equilibrium partitioning theory, the properties of organic aerosol once formed may differ significantly from the properties determined in the equilibrium framework.
194 citations
TL;DR: In this paper, the authors performed a series of cosmological simulations using Enzo, an Eulerian adaptive-mesh refinement, N-body + hydrodynamical code, applied to study the warm/hot intergalactic medium (WHIM).
Abstract: We perform a series of cosmological simulations using Enzo, an Eulerian adaptive-mesh refinement, N-body + hydrodynamical code, applied to study the warm/hot intergalactic medium (WHIM). The WHIM may be an important component of the baryons missing observationally at low redshift. We investigate the dependence of the global star formation rate and mass fraction in various baryonic phases on spatial resolution and methods of incorporating stellar feedback. Although both resolution and feedback significantly affect the total mass in the WHIM, all of our simulations find that the WHIM fraction peaks at z ~ 0.5, declining to 35%-40% at z = 0. We construct samples of synthetic O VI absorption lines from our highest-resolution simulations, using several models of oxygen ionization balance. Models that include both collisional ionization and photoionization provide excellent fits to the observed number density of absorbers per unit redshift over the full range of column densities (1013 cm?2 N O VI 1015 cm?2). Models that include only collisional ionization provide better fits for high column density absorbers (N O VI 1014 cm?2). The distribution of O VI in density and temperature exhibits two populations: one at T ~ 105.5 K (collisionally ionized, 55% of total O VI) and one at T ~ 104.5 K (photoionized, 37%) with the remainder located in dense gas near galaxies. While not a perfect tracer of hot gas, O VI provides an important tool for a WHIM baryon census.
146 citations
TL;DR: It is found that the photoelectrons carry linear momentum corresponding to the photons absorbed above the field free ionization threshold, which has implications for concurrent models of the generation of terahertz radiation in filaments.
Abstract: The balance of the linear photon momentum in multiphoton ionization is studied experimentally. In the experiment argon and neon atoms are singly ionized by circularly polarized laser pulses with a wavelength of 800 and 1400 nm in the intensity range of ${10}^{14}--{10}^{15}\text{ }\text{ }\mathrm{W}/{\mathrm{cm}}^{2}$. The photoelectrons are measured using velocity map imaging. We find that the photoelectrons carry linear momentum corresponding to the photons absorbed above the field free ionization threshold. Our finding has implications for concurrent models of the generation of terahertz radiation in filaments.
143 citations
TL;DR: It is shown theoretically that the photoionization process in a hollow-core photonic crystal fiber filled with a Raman-inactive noble gas leads to a constant acceleration of solitons in the time domain with a continuous shift to higher frequencies, opposite to the well-known Raman self-frequency redshift of sol itons in solid-core glass fibers.
Abstract: We show theoretically that the photoionization process in a hollow-core photonic crystal fiber filled with a Raman-inactive noble gas leads to a constant acceleration of solitons in the time domain with a continuous shift to higher frequencies, limited only by ionization loss. This phenomenon is opposite to the well-known Raman self-frequency redshift of solitons in solid-core glass fibers. We also predict the existence of unconventional long-range nonlocal soliton interactions leading to spectral and temporal soliton clustering. Furthermore, if the core is filled with a Raman-active molecular gas, spectral transformations between redshifted, blueshifted, and stabilized solitons can take place in the same fiber.
125 citations
TL;DR: In experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse train in the presence of a near-infrared field, the ionization probability is sensitive to the instantaneous polarization of the molecule by the IR electric field and this work demonstrates that it has probed the IR-induced electron dynamics withAttosecond pulses.
Abstract: We report experiments where hydrogen molecules were dissociatively ionized by an attosecond pulse train in the presence of a near-infrared field. Fragment ion yields from distinguishable ionization channels oscillate with a period that is half the optical cycle of the IR field. For molecules aligned parallel to the laser polarization axis, the oscillations are reproduced in two-electron quantum simulations, and can be explained in terms of an interference between ionization pathways that involve different harmonic orders and a laser-induced coupling between the 1s sigma(g) and 2p sigma(u) states of the molecular ion. This leads to a situation where the ionization probability is sensitive to the instantaneous polarization of the molecule by the IR electric field and demonstrates that we have probed the IR-induced electron dynamics with attosecond pulses. (Less)
119 citations
TL;DR: In this paper, a detailed computational modeling study of a luminous plasma jet discharge is presented, where the dynamics of streamer propagation, its dependence on the diffusional mixing layer between helium and air species, and the role of photoionization are discussed.
Abstract: A luminous plasma jet is produced when helium gas issuing into atmospheric pressure ambient air is excited by high voltage nanosecond pulsing of a dielectric covered electrode. A detailed computational modeling study of such a discharge is presented. The dynamics of streamer propagation, its dependence on the diffusional mixing layer between helium and air species, and the role of photoionization are discussed.
TL;DR: Both experimental and modeling results indicate that few aromatics could be formed in these flames, and a new mechanism involving 206 species and 1368 reactions has been proposed whose predictions are in reasonable agreement with measured species profiles for the three investigated flames.
TL;DR: In this article, the spectral shape of the terahertz (THz) pulses generated by this mechanism is determined by the superposition of contributions from individual ionization events, which provides a straightforward analogy to linear diffraction theory, where the ionisation events play the role of slits in a grating.
Abstract: Various applications ranging from nonlinear terahertz (THz) spectroscopy to remote sensing require broadband and intense THz radiation, which can be generated by focusing two-color laser pulses into a gas. In this setup, THz radiation originates from the buildup of electron density in sharp steps of attosecond duration due to tunnel ionization, and the subsequent acceleration of free electrons in the laser field. We show that the spectral shape of the THz pulses generated by this mechanism is determined by the superposition of contributions from individual ionization events. This provides a straightforward analogy to linear diffraction theory, where the ionization events play the role of slits in a grating. This analogy offers simple explanations for recent experimental observations and opens new avenues for THz pulse shaping based on temporal control of the ionization events. We illustrate this novel technique by tailoring the spectral width and position of the resulting radiation using multi-color pump pulses.
TL;DR: In this article, a straightforward extension of Young's double-slit interferences leads to oscillations in corresponding vibrational ratios, showing that the molecules behave as two-center electron-wave emitters and that the associated interferences leave their trace in the angle-integrated photoionization cross section.
Abstract: Vibrationally resolved valence-shell photoionization spectra of H 2 , N 2 and CO have been measured in the photon energy range 20–300 eV using third-generation synchrotron radiation. Young’s double-slit interferences lead to oscillations in the corresponding vibrational ratios, showing that the molecules behave as two-center electron-wave emitters and that the associated interferences leave their trace in the angle-integrated photoionization cross section. In contrast to previous work, the oscillations are directly observable in the experiment, thereby removing any possible ambiguity related to the introduction of external parameters or fitting functions. A straightforward extension of an original idea proposed by Cohen and Fano [Cohen HD, Fano U (1966) Phys Rev 150:30] confirms this interpretation and shows that it is also valid for diatomic heteronuclear molecules. Results of accurate theoretical calculations are in excellent agreement with the experimental findings.
TL;DR: In this article, blue-detuned optical traps are proposed for trapping ground-state and Rydberg excited atoms, which are suitable for trapping both groundstate and excited atoms.
Abstract: We propose blue-detuned optical traps that are suitable for trapping of both ground-state and Rydberg excited atoms The addition of a background compensation field or a suitable choice of the trap geometry provides a magic trapping condition for ground-state and Rydberg atoms at the trap center Deviations from the magic condition at finite temperature are calculated Designs that achieve less than 200-kHz differential trap shift between Cs ground states and $125s$ Rydberg states for 10 $\ensuremath{\mu}\mathrm{K}$ Cs atoms are presented Consideration of the trapping potential and photoionization rates suggests that these traps will be useful for quantum-information experiments with atomic qubits
TL;DR: A conceptual framework for time-resolved photoionization measurements is presented, together with discussion of relevant theory for the different aspects of TRPES, and simple models are used to illustrate the theory and key concepts are amplified by experimental examples.
Abstract: Time-resolved photoelectron spectroscopy (TRPES) is a powerful tool for the study of intramolecular dynamics, particularly excited state non-adiabatic dynamics in polyatomic molecules. Depending on the problem at hand, different levels of TRPES measurements can be performed: time-resolved photoelectron yield; time- and energy-resolved photoelectron yield; time-, energy-, and angle-resolved photoelectron yield. In this pedagogical overview, a conceptual framework for time-resolved photoionization measurements is presented, together with discussion of relevant theory for the different aspects of TRPES. Simple models are used to illustrate the theory, and key concepts are further amplified by experimental examples. These examples are chosen to show the application of TRPES to the investigation of a range of problems in the excited state dynamics of molecules: from the simplest vibrational wavepacket on a single potential energy surface; to disentangling intrinsically coupled electronic and nuclear motions; to identifying the electronic character of the intermediate states involved in non-adiabatic dynamics by angle-resolved measurements in the molecular frame, the most complete measurement.
TL;DR: The state-of-the-art in the employment of soft ionization techniques for CE-MS is presented and the principle of each ionization technique is outlined and the experimental set-ups of the CE- MS couplings are described.
Abstract: A major step forward in the development and application of capillary electrophoresis (CE) was its coupling to ESI-MS, first reported in 1987. More than two decades later, ESI has remained the principal ionization technique in CE-MS, but a number of other ionization techniques have also been implemented. In this review the state-of-the-art in the employment of soft ionization techniques for CE-MS is presented. First the fundamentals and general challenges of hyphenating conventional CE and microchip electrophoresis with MS are outlined. After elaborating on the characteristics and role of ESI, emphasis is put on alternative ionization techniques including sonic spray ionization (SSI), thermospray ionization (TSI), atmospheric pressure chemical ionization (APCI), atmospheric pressure photoionization (APPI), matrix-assisted laser desorption ionization (MALDI) and continuous-flow fast atom bombardment (CF-FAB). The principle of each ionization technique is outlined and the experimental set-ups of the CE-MS couplings are described. The strengths and limitations of each ionization technique with respect to CE-MS are discussed and the applicability of the various systems is illustrated by a number of typical examples.
TL;DR: It is found that interchannel coupling not only affects the hole populations, but it also enhances the entanglement between the photoelectron and the remaining ion, thereby reducing the coherence within the ion.
Abstract: The creation of superpositions of hole states via single-photon ionization using attosecond extreme-ultraviolet pulses is studied with the time-dependent configuration-interaction singles (TDCIS) method. Specifically, the degree of coherence between hole states in atomic xenon is investigated. We find that interchannel coupling not only affects the hole populations, but it also enhances the entanglement between the photoelectron and the remaining ion, thereby reducing the coherence within the ion. As a consequence, even if the spectral bandwidth of the ionizing pulse exceeds the energy splittings among the hole states involved, perfectly coherent hole wave packets cannot be formed. For sufficiently large spectral bandwidth, the coherence can only be increased by increasing the mean photon energy.
TL;DR: In this paper, the trap-induced shift of the two-photon microwave transition was analyzed using lattice-induced photoionization, and the dependence of the efficiency on the timing of the lattice inversion and on the trap laser power was studied.
Abstract: Rubidium Rydberg atoms are laser excited and subsequently trapped in a one-dimensional optical lattice (wavelength 1064 nm). Efficient trapping is achieved by a lattice inversion immediately after laser excitation using an electro-optic technique. The trapping efficiency is probed via analysis of the trap-induced shift of the two-photon microwave transition $50S\ensuremath{\rightarrow}51S$. The inversion technique allows us to reach a trapping efficiency of 90%. The dependence of the efficiency on the timing of the lattice inversion and on the trap laser power is studied. The dwell time of $50{D}_{5/2}$ Rydberg atoms in the lattice is analyzed using lattice-induced photoionization.
TL;DR: In this article, the Cooper minimum in high-order-harmonic generation from argon atoms by using long wavelength laser pulses was studied and shown to be systematically shifted with respect to total photoionization cross section measurements.
Abstract: We study the Cooper minimum in high-order-harmonic generation from argon atoms by using long wavelength laser pulses. We find that the minimum in high-order-harmonic spectra is systematically shifted with respect to total photoionization cross section measurements. We use a semiclassical theoretical approach based on classical trajectory Monte Carlo and quantum electron scattering methods to model the experiment. Our study reveals that the shift between photoionization and high-order-harmonic emission is due to several effects: the directivity of the recombining electrons and emitted polarization, and the shape of the recolliding electron wave packet.
TL;DR: In this article, the authors obtained deep, high spatial and spectral resolution, long-slit spectra of the Halpha nebulae in the cool cores of 9 galaxy clusters.
Abstract: We have obtained deep, high spatial and spectral resolution, long-slit spectra of the Halpha nebulae in the cool cores of 9 galaxy clusters. This sample provides a wealth of information on the ionization state, kinematics, and reddening of the warm gas in the cool cores of galaxy clusters. We find evidence for only small amounts of reddening in the extended, line-emitting filaments, with the majority of filaments having E(B-V) < 0.2. The combination of [O III]/Hb, [N II]/Ha, [S II]/Ha, and [O I]/Ha allow us to rule out collisional ionization by cosmic rays, thermal conduction, and photoionization by ICM X-rays and AGN as strong contributors to the ionization of the warm gas in both nuclei and filaments. The data are adequately described by a composite model of slow shocks and star formation. This model is further supported by an observed correlation between the linewidths and low ionization line ratios which becomes stronger in systems with more modest star formation activity based on far ultraviolet observations. We find that the more extended, narrow filaments tend to have shallower velocity gradients and narrower linewidths than the compact filamentary complexes. We confirm that the widths of the emission lines decrease with radius, from FWHM \sim 600 km/s in the nuclei to FWHM ~ 100 km/s in the most extended filaments. We suggest that this radial dependence of the velocity width may in fact be linked to ICM turbulence and, thus, may provide a glimpse into the amount of turbulence in cool cores. In the central regions (r < 10 kpc) of several systems the warm gas shows kinematic signatures consistent with rotation. We find that the kinematics of the most extended filaments in this sample are broadly consistent with both infall and outflow, and recommend further studies linking the warm gas kinematics to both radio and X-ray maps in order to further understand the observed kinematics.
TL;DR: The ultrafast dynamics of the cationic hole formed in bulk liquid water following ionization is investigated by ab initio molecular dynamics simulations and an experimentally accessible signature is suggested that might be tracked by femtosecond pump-probe spectroscopy.
Abstract: The ultrafast dynamics of the cationic hole formed in bulk liquid water following ionization is investigated by ab initio molecular dynamics simulations and an experimentally accessible signature is suggested that might be tracked by femtosecond pump-probe spectroscopy. This is one of the fastest fundamental processes occurring in radiation-induced chemistry in aqueous systems and biological tissue. However, unlike the excess electron formed in the same process, the nature and time evolution of the cationic hole has been hitherto little studied. Simulations show that an initially partially delocalized cationic hole localizes within ~30 fs after which proton transfer to a neighboring water molecule proceeds practically immediately, leading to the formation of the OH radical and the hydronium cation in a reaction which can be formally written as H(2)O(+) + H(2)O → OH + H(3)O(+). The exact amount of initial spin delocalization is, however, somewhat method dependent, being realistically described by approximate density functional theory methods corrected for the self-interaction error. Localization, and then the evolving separation of spin and charge, changes the electronic structure of the radical center. This is manifested in the spectrum of electronic excitations which is calculated for the ensemble of ab initio molecular dynamics trajectories using a quantum mechanics/molecular mechanics (QM∕MM) formalism applying the equation of motion coupled-clusters method to the radical core. A clear spectroscopic signature is predicted by the theoretical model: as the hole transforms into a hydroxyl radical, a transient electronic absorption in the visible shifts to the blue, growing toward the near ultraviolet. Experimental evidence for this primary radiation-induced process is sought using femtosecond photoionization of liquid water excited with two photons at 11 eV. Transient absorption measurements carried out with ~40 fs time resolution and broadband spectral probing across the near-UV and visible are presented and direct comparisons with the theoretical simulations are made. Within the sensitivity and time resolution of the current measurement, a matching spectral signature is not detected. This result is used to place an upper limit on the absorption strength and/or lifetime of the localized H(2)O(+) ((aq)) species.
TL;DR: In this article, the multiconfigurational time-dependent Hartree-Fock method (MCTDHF) is applied for simulations of the two-photon ionization of helium.
Abstract: The multiconfigurational time-dependent Hartree–Fock method (MCTDHF) is applied for simulations of the two-photon ionization of helium. We present results for the single and double ionizations from the ground state for photon energies in the nonsequential regime and compare them to direct solutions of the Schrodinger equation using the time-dependent (full) configuration interaction (TDCI) method. We find that the single ionization is accurately reproduced by MCTDHF, whereas the double ionization results correctly capture the main trends of TDCI.
TL;DR: The dynamics of two distinct regimes: ionization induced blue-shift and resonant dispersive wave emission in the deep-UV are considered and it is illustrated how the system evolves between these regimes and the changing influence of ionization.
Abstract: We numerically investigate the effect of ionization on ultrashort high-energy pulses propagating in gas-filled kagome-lattice hollow-core photonic crystal fibers by solving an established uni-directional field equation. We consider the dynamics of two distinct regimes: ionization induced blue-shift and resonant dispersive wave emission in the deep-UV. We illustrate how the system evolves between these regimes and the changing influence of ionization. Finally, we consider the effect of higher ionization stages.
TL;DR: In this paper, a method for determination of physical conditions in the broad line regions of a significant subsample of Seyfert-1 nuclei and quasars is described.
Abstract: We describe a method for determination of physical conditions in the broad line regions of a significant subsample of Seyfert-1 nuclei and quasars. Several diagnostic ratios based on intermediate (AlIII 1860, SiIII 1892) and high (CIV 1549, SiIV 1397) ionization lines in the UV spectra of quasars are used to constrain density, ionization and metallicity of the emitting gas. We apply the method to two extreme Population A quasars - the prototypical NLSy1 I Zw 1 and a high-z\ NLSy1-like object, SDSS J120144.36+011611.6. We find well-defined physical conditions: low ionization (ionization parameter $< 10^{-2}$), high density (10$^{12} - 10^{13}$ cm^{-3}) and significant metal enrichment. Ionization parameter and density can be derived independently for each source with an uncertainty that is always less than $\pm 0.3$ in logarithm. We use the product density times ionization parameter to estimate the broad line region radius and the virial black hole mass. Estimates of black hole masses based on the "photoionization" analysis described in this paper are probably more accurate than those derived from the radius - luminosity correlation.
TL;DR: The single center (SC) method for computation of highly-delocalized discrete and partial photoelectron wave continuous functions of molecules is discussed and its potential for theoretically studying angularly resolved molecular photoionization processes is demonstrated.
Abstract: We discuss the recent progress in the development of the single center (SC) method for computation of highly-delocalized discrete and partial photoelectron wave continuous functions of molecules. Basic equations of the SC method are presented, and an efficient scheme for the numerical solution of a system of coupled Hartree–Fock equations for a photoelectron is described. Several illustrative applications of the method to photoionization and electronic excitation processes in diatomic molecules are considered. Thereby, we demonstrate its potential for theoretically studying angularly resolved molecular photoionization processes.
01 Jan 2011
TL;DR: In this article, the authors present an overview of the atomic structure of galaxies and their properties and spectra, including absorption lines, radiative transfer, photoionization, and recombination.
Abstract: 1. Introduction 2. Atomic structure 3. Atomic processes 4. Radiative transitions 5. Electron-ion collisions 6. Photoionization 7. Electron-ion recombination 8. Multi-wavelength emission lines 9. Absorption lines and radiative transfer 10. Stellar properties and spectra 11. Stellar opacity and radiative forces 12. Gaseous nebulae and HII regions 13. Active galactic nuclei and quasars 14. Cosmology Appendices References Index.
Journal Article•
TL;DR: Vibrational progressions for the S(0)-D(0) vibronic bands computed within double-harmonic approximation with Duschinsky rotations are compared with previously reported experimental photoelectron spectra and differentiated PIE curves.
Abstract: Electronic structure and spectroscopy of nucleic acid bases: Ionization energies, ionization-induced structural changes, and photoelectron spectra Ksenia B. Bravaya a , Oleg Kostko b , Stanislav Dolgikh a , Arie Landau a , Musahid Ahmed b , and Anna I. Krylov a a Department of Chemistry, University of Southern California, Los Angeles, CA 90089-0482, USA b Chemical Sciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA We report high-level ab initio calculations and single-photon ionization mass spec- trometry study of ionization of adenine (A), thymine (T), cytosine (C) and guanine (G). For thymine and adenine, only the lowest-energy tautomers were considered, whereas for cytosine and guanine we characterized five lowest-energy tautomeric forms. The first adiabatic and several vertical ionization energies were computed us- ing equation-of-motion coupled-cluster method for ionization potentials with single and double substitutions. Equilibrium structures of the cationic ground states were characterized by DFT with the ωB97X-D functional. The ionization-induced geome- try changes of the bases are consistent with the shapes of the corresponding molecular orbitals. For the lowest-energy tautomers, the magnitude of the structural relaxation decreases in the following series G>C>A>T, the respective relaxation energies being 0.41, 0.32, 0.25 and 0.20 eV. The computed adiabatic ionization energies (8.13, 8.89, 8.51-8.67 and 7.75-7.87 eV for A,T,C and G, respectively) agree well with the on- sets of the photoionization efficiency (PIE) curves (8.20±0.05, 8.95±0.05, 8.60±0.05 and 7.75±0.05 eV). Vibrational progressions for the S 0 -D 0 vibronic bands computed within double-harmonic approximation with Duschinsky rotations are compared with previously reported experimental photoelectron spectra. I. INTRODUCTION Ionization of DNA bases is one of the processes involved in DNA radiation- and photo- damage resulting in dangerous mutations with potential risk for cancer and neurodegenera-
TL;DR: The aromatic indene molecule (C9H8) together with its acyclic isomers (phenylallene, 1-phenyl-1-propyne, and 3-phenylon-1propynes) were formed via a "directed synthesis" in situ utilizing a high-temp...
Abstract: The aromatic indene molecule (C9H8) together with its acyclic isomers (phenylallene, 1-phenyl-1-propyne, and 3-phenyl-1-propyne) were formed via a “directed synthesis” in situ utilizing a high-temp...
TL;DR: It is shown how a resonance embedded in the molecular continuum dramatically affects the phases of the two-photon transition amplitudes, opening the way to attosecond time-resolved measurements, equivalent to double-slit experiments in the time domain.
Abstract: We have simulated two-color photoionization of N 2 by solving the time-dependent Schrodinger equation with a simple model accounting for the correlated vibronic dynamics of the molecule and of the ion N þ 2. Our results, in very good agreement with recent experiments [Haessler et al., Phys. Rev. A 80, 011404 (2009)], show how a resonance embedded in the molecular continuum dramatically affects the phases of the two-photon transition amplitudes. In addition, we introduce a formal relation between these measurable phases and the photoelectron release time, opening the way to attosecond time-resolved measurements, equivalent to double-slit experiments in the time domain.