Autoionizing States Research Articles

Inelastic resonant scattering of electrons on hydrogen-like ions

Abstract The inelastic electron scattering is one of the processes that must be understood in detail for the correct interpretation of astrophysical data. We suggest ab initio QED treatment of the inelastic scattering of quasi-free electrons on hydrogen-like ions with possible formation and subsequent decay of intermediate autoionizing states. We calculate the doubly differential cross sections for scattering on F8+, Ca19+ and Kr35+ in the range of energies where doubly excited 3l3l' states are involved. The energies and widths of these states are presented.

Satellite lines from auto-ionizing states of Fe xvi and the problems with the X-ray Fe xvii lines

ABSTRACT We present new calculations of atomic data needed to model auto-ionizing states of Fe xvi. We compare the state energies, radiative and excitation data with a sample of results from previous literature. We find a large scatter of results, the most significant ones in the auto-ionization rates, which are very sensitive to the configuration interaction and state mixing. We find relatively good agreement between the auto-ionization rates and the collisional excitation rates calculated with the R-matrix suite of programs and autostructure. The largest model, which includes J-resolved states up to $n=10$, produces ab-initio wavelengths and intensities of the satellite lines which agree well with solar high-resolution spectra of active regions, with few minor wavelength adjustments. We review previous literature, finding many incorrect identifications, most notably those in the NIST data base. We provide several new tentative identifications in the 15–15.7 Å range, and several new ones at shorter wavelengths, where previous lines were unidentified. Compared to the previous CHIANTI model, the present one has an increased flux in the 15–15.7 Å range at 2 MK of a factor of 1.9, resolving the discrepancies found in the analysis of the Marshall Grazing Incidence X-Ray Spectrometer observation. It appears that the satellite lines also resolve the long-standing discrepancy in the intensity of the important Fe xvii 3D line at 15.26 Å.

Trapping Ba+ with seven-fold enhanced efficiency utilizing an autoionizing resonance

Trapped ions have emerged as a front runner in quantum information processing due to their identical nature, all-to-all connectivity, and high fidelity quantum operations. As current trapped ion technologies are scaled, it will be important to improve the efficiency of loading ions, especially when working with long chains of ions or rare isotopes. Here, we compare two different isotope-selective photoionization schemes for loading 138Ba+ ions. We show that a two-step photoionization scheme ending in an autoionizing transition increases the ion loading rate nearly an order of magnitude compared to an established technique which does not excite an autoionizing state. Our novel photoionization scheme can be extended to all isotopes of barium. Given that autoionizing resonances exist in every trapped ion species, exploitation of this process is a promising pathway to increase the loading rates for trapped ion computers.

Resonant laser ionization of neptunium: investigation on excitation schemes and the first ionization potential

The atomic structure of neptunium (Np) was investigated by two-step resonance ionization spectroscopy. The study involved exploring ground-state transitions as well as following transitions to high-lying states just below the ionization potential (IP) or auto-ionizing states above the IP. That resulted in the identification of two-step ionization schemes, suitable for trace analysis and nuclear structure investigations. The lifetimes of two excited states located at 25,342.48 cm-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\, \ ext {cm}^{-1} $$\\end{document} and 25,277.64 cm-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\, \ ext {cm}^{-1} $$\\end{document} were determined as 230(12) ns and 173(9) ns, respectively. Because of the absence of Rydberg series in wide-ranging spectra recorded, the first IP was determined through the field ionization of high-lying, weakly-bound states using a well-controlled static electric field. By applying the saddle-point model, an IP value of 50,535.54(15) cm-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document} [6.265608(19) eV] was derived. This value agrees with the current literature value of 50,535(2) cm-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$^{-1}$$\\end{document}, while providing a more than ten times higher precision.Graphic abstract

New Data on Autoionizing States of Ne Induced by Low-Energy Electrons from 45 to 64 eV

The lowest single and doubly excited autoionizing states of neon have been studied using a non-monochromatic electron beam and a high-resolution electrostatic analyzer at incident electron energies from 43.37 to 202 (±0.4) eV at three ejection angles, 40°, 90° and 130°. The 2s2p63s(3,1S) and 2s2p63p(3,1P) as well as the 2p43s3p doubly excited states have been observed and their energy determined. The influence of the PCI effect in the energy region of the 2s2p63s(3,1S) states has been investigated. New features in the ejected electron spectra in the low kinetic energy region 3–20 eV at 202 eV incident energy have been observed and assigned.

Contribution of molecular orbital promotion to the electronic stopping cross section at slow atom solid collisions

The autoionization states formation due to MO promotion during collisions of keV-energy ions with solids produces a dominant contribution to inelastic energy losses and, accordingly, to the electronic stopping powers dE/dx. The correlations of emitted electron numbers δ with the values of inelastic energy losses Q are shown. When corresponding distances of closest approach are reached, the MO orbital promotion produces a stepwise increase in values of Q and δ. Based on the measured ionization cross-sections and Q values, electronic stopping powers can be calculated. For the case when such measurements are not available, the scaling for the ionization cross section in the case of K, L and M shell excitation can be used.We have proposed a new model for calculating electronic stopping power in which the formation of autoionization states in atomic collisions makes a dominant contribution to the inelastic energy loss and ionization of colliding atoms. Using data on the values of energy losses and ionization cross sections, it is possible to calculate the values of electronic stopping. The model predicts the threshold character of the dE/dx dependence versus the collision velocity and an increase in inelastic energy losses at the collision energies at which the threshold for the corresponding MO promotion occurs.

Contribution of molecular orbital promotion to the electronic stopping cross section at slow atom solid collisions

The autoionization states formation due to MO promotion during collisions of keV-energy ions with solids produces a dominant contribution to inelastic energy losses and, accordingly, to the electronic stopping powers dE/dx. The correlations of emitted electron numbers δ with the values of inelastic energy losses Q are shown. When corresponding distances of closest approach are reached, the MO orbital promotion produces a stepwise increase in values of Q and δ. Based on the measured ionization cross-sections and Q values, electronic stopping powers can be calculated. For the case when such measurements are not available, the scaling for the ionization cross section in the case of K, L and M shell excitation can be used.We have proposed a new model for calculating electronic stopping power in which the formation of autoionization states in atomic collisions makes a dominant contribution to the inelastic energy loss and ionization of colliding atoms. Using data on the values of energy losses and ionization cross sections, it is possible to calculate the values of electronic stopping. The model predicts the threshold character of the dE/dx dependence versus the collision velocity and an increase in inelastic energy losses at the collision energies at which the threshold for the corresponding MO promotion occurs.

Effect of Absorption and Polarization Potentials in The Distorted Wave Calculation of Positron Impact Excitation of Autoionizing State of Rubidium

This study focuses on the scattering of positrons and rubidium atoms. We utilized the distorted wave approach to compute the cross sections and alignment parameter from near excitation threshold up to 1500 eV. Our system employed Clementi and Roetti (1974) multi-zeta Roothan-Hatree-Fock wave. We employed a complex distortion potential comprising static, absorption, and polarization terms to calculate cross sections and the alignment parameter. Our results were compared with other available studies, and we found that including polarization and absorption potentials significantly affected the cross-sections and the alignment parameter, especially at low-impact energies. These two potentials enhanced the accuracy of both the cross-section and alignment parameter results.

Pathways to the Local Thermodynamic Equilibrium of Complex Autoionizing States

The generally accepted pathway to Local Thermodynamic Equilibrium (LTE) in atomic physics, where collision rates need to be much larger than radiative decay rates, is extended to complex autoionizing states. It is demonstrated that the inclusion of the non-radiative decay (autoionization rate) on the same footing, like radiative decay, i.e., the LTE criterion ne,crit×C≫A+Γ (ne,crit is the critical electron density above which LTE holds, C is the collisional rate coefficient, and A is the radiative decay rate) is inappropriate for estimating the related critical density. An analysis invoking simultaneously different atomic ionization stages identifies the LTE criteria as a theoretical limiting case, which provides orders of magnitude too high critical densities for almost all practical applications. We introduced a new criterion, where the critical densities are estimated from the non-autoionizing capture states rather than from the autoionizing states. The new criterion is more appropriate for complex autoionizing manifolds and provides order of magnitude reduced critical densities. Detailed numerical calculations are carried out for Na-like states of aluminum, where autoionization to the Ne-like ground and excited state occurrences are in excellent agreement with the new criterion. In addition, a complex multi-electron atomic-level structure and electron–electron correlation are identified as simplifying features rather than aggravating ones for the concept of thermalization.

Symmetric Fano Profiles of Two-photon Electronic Transitions Observed in an Ultracold Rydberg Gas

Fano profiles are caused by the interference between the discrete states and continuum. It is a very common phenomenon
 in multi-electron Rydberg states, such as the Rydberg states of group II elements in the periodic table. It often leads to
 autoionization due to the fact that a discrete state couples with an autoionizing state. Unlike the typical asymmetric line
 shape, here we report a symmetric unusual Fano line shape that has been predicted. In addition, this profile is caused
 by molecular states or polymer states instead of multi-electron atomic states. Moreover, it is shown that the fano profile
 caused by the multi-electron polymer states does not necessarily lead to autoionization. We propose that the Fano profile
 studied is caused by the interference between discrete levels and the multipole-multipole coupled continuum, or energy
 band.

Directly imaging excited state-resolved transient structures of water induced by valence and inner-shell ionisation

Real-time imaging of transient structure of the electronic excited state is fundamentally critical to understand and control ultrafast molecular dynamics. The ejection of electrons from the inner-shell and valence level can lead to the population of different excited states, which trigger manifold ultrafast relaxation processes, however, the accurate imaging of such electronic state-dependent structural evolutions is still lacking. Here, by developing the laser-induced electron recollision-assisted Coulomb explosion imaging approach and molecular dynamics simulations, snapshots of the vibrational wave-packets of the excited (A) and ground states (X) of D2O+ are captured simultaneously with sub-10 picometre and few-femtosecond precision. We visualise that θDOD and ROD are significantly increased by around 50∘ and 10 pm, respectively, within approximately 8 fs after initial ionisation for the A state, and the ROD further extends 9 pm within 2 fs along the ground state of the dication in the present condition. Moreover, the ROD can stretch more than 50 pm within 5 fs along autoionisation state of dication. The accuracies of the results are limited by the simulations. These results provide comprehensive structural information for studying the fascinating molecular dynamics of water, and pave the way towards to make a movie of excited state-resolved ultrafast molecular dynamics and light-induced chemical reaction.

Obrazovanie i raspad avtoionizatsionnykh sostoyaniy - osnovnoy mekhanizm neuprugikh poter' pri stolknoveniyakh atomov keV-energiy

It has been shown that the formation of autoionization states makes the dominant contribution to inelastic energy loss and to ionization in keV atomic collisions, i.e., at velocities lower than the velocities of atomic electrons. Scaling laws have been proposed to calculate the cross sections for the formation of vacancies in inner K and L electron shells of colliding atoms. A model has been proposed to relate ionization processes and the observed inelastic energy losses. Auger transitions in a short-lived quasimolecule formed by two atoms approaching each other have been studied. The nature of the continuous component in electron spectra emitted in collisions has been determined. It has been shown that the excitation of autoionization states determines the stopping cross sections for keV atoms in matter.

Dark and bright autoionizing states in resonant high-order harmonic generation: Simulation via a one-dimensional helium model

We study the role of dark and bright autoionizing states (AIS) in photoionization and high harmonic generation (HHG) using a 1D helium model. This model allows numerical integration of the time-dependent Schr\"odinger equation beyond the singe-electron approximation completely taking into account electronic correlation. We find the level structure of the system and the spatial distribution of the electronic density for several states including AIS. Studying the HHG efficiency as a function of the detuning from the resonances with AIS we find the HHG enhancement lines. The shapes of these lines are different from the corresponding Fano lines in the photoelectronic spectra, in agreement with the experimental studies in helium. Moreover, we simulate HHG under the conditions when the fundamental frequency is close to the even-order multiphoton resonance with the dark AIS. We find the enhanced generation of the neighbouring odd harmonics. The details of the enhancement lines for these harmonics can be understood taking into account the temporal delay between the emission of the non-resonant and resonant XUV; this delay is defined by the AIS lifetime. Finally, our simulations show that the HHG enhancement due to the dark and the bright AIS is comparable in the studied system.

Laser ionization scheme development for in-gas-jet spectroscopy studies of Th+

The in-gas laser ionization and spectroscopy (IGLIS) technique has been a cornerstone in the study of heavy elements. The addition of a convergent–divergent (de Laval) nozzle to perform laser ionization in a cold hypersonic gas jet greatly improves the achievable resolution. Recent efforts have focused on preparing the in-gas-jet method for the study of the low-lying 229Th isomer. Tailor-made recoil sources of 233U are installed inside a fast extraction gas cell to provide the (isomeric) thorium ions. A level search above the second ionization potential (IP) uncovered several auto-ionizing states, greatly improving the laser ionization efficiency of singly charged thorium ions.

Formation and Decay of Autoionization States as the Main Inelastic Energy Loss Mechanism in keV Atomic Collisions

Formation and Decay of Autoionization States as the Main Inelastic Energy Loss Mechanism in keV Atomic Collisions

Ultrafast Resonant State Formation by the Coupling of Rydberg and Dark Autoionizing States.

Studying the dynamics of dark states is challenging due to their inability to undergo single-photon emission or absorption. This challenge is made even more difficult for dark autoionizing states owing to their ultrashort lifetime of a few femtoseconds. High-order harmonic spectroscopy recently appeared as a novel method to probe the ultrafast dynamics of a single atomic or molecular state. Here, we demonstrate the emergence of a new type of ultrafast resonance state as a manifestation of coupling between Rydberg and a dark autoionizing state dressed by a laser photon. Through high-order harmonic generation, this resonance results in extreme ultraviolet light emission that is more than one order of magnitude stronger than for the off-resonance case. The induced resonance can be leveraged to study the dynamics of a single dark autoionizing state and the transient changes in the dynamics of real states due to their overlap with the virtual laser-dressed states. In addition, the present results allow the generation of coherent ultrafast extreme ultraviolet light for advanced ultrafast science applications.

High-useful yield and new autoionizing state of resonantly ionized tungsten

This work presents a new RIS scheme for W with ∼15% useful yield using three tunable Ti:Sa lasers as determined by conducting spectroscopic surveys and saturation experiments.

Singly Resonant Multiphoton Processes Involving Autoionizing States in the Be-like CIII Ion

In this paper, we investigate the applicability of different theories on the intensity-dependent ionization rate for C2+ atomic targets at different laser wavelengths (frequency) and at linear polarization. We use the analytical formulas and draw conclusions, from numerical comparison with the results from ab initio ‘two-state model’ R-matrix Floquet calculation, on their correct predictions of the ionization rate. The single-photon ionization has been studied in the vicinity of the 1s2 (2Po)2pns (1Po), n = 5–12 autoionizing resonances at non-perturbative laser intensity. The results obtained from Perelomov–Popov–Terent’ev and Ammosov–Delone–Krainov models are compared in a region away from resonance where the two-state model description is not as good. To quantify the deviation between theoretical models, we analyze the ratio between different data sets as functions of the Keldysh parameter. We conclude that the results obtained with the model of Perelemov–Popov–Terent’ev are the closest to the ab initio R-matrix Floquet calculation.

Electron-Impact Excitation of the λ190.8 nm and λ179.9 nm Intercombination Lines in the Tl+ Ion

The results of experimental and theoretical studies on electron-impact excitation of the 6s6p P1° 3→6s2 S0 1 (λ190.8 nm) and 6s7s S0 1→6s6p P1° 3 (λ179.9 nm) intercombination transitions in the single-charged thallium ion are presented. The crossed-beams technique was used in combination with a spectroscopic method in the experiment. A distinct structure revealed in the cross-sections of both lines results from electron decay of atomic autoionizing states and radiative transitions from upper ionic levels. The dominant mechanism of the structure formation was the Coster–Kronig process. Relativistic distorted wave calculations were performed to obtain emission cross-sections for the above transitions. The absolute values of the cross-sections were found to be (0.25 ± 0.08) × 10−16 cm2 (λ190.8 nm) and (0.10 ± 0.04) × 10−16 cm2 (λ179.9 nm) at the electron energy of 100 eV.

Numerical studies of isotopic selective photoionization of ytterbium in a three-step ionization scheme

Selective photoionization of ytterbium isotope is studied numerically based on a three-step photoionization scheme, 4f146s2 1S0 (0 cm−1) → 4f146s6p 3P1 (17992.008 cm−1) → (4f136s26p) (7/2, 3/2)2 (35196.98 cm−1) → auto-ionization state (52353 cm−1) → Yb+, by the density matrix theory with the consideration of atomic hyperfine structures and magnetic sublevels. To examine the physical model, the numerical isotopic abundance of ytterbium is compared with that from mass spectroscopy experiment, showing that they are in good agreement with each other. The excitation process and ionization process of ytterbium, especially for odd isotopes, are discussed and analyzed in detail on this basis. The effects of frequency detuning, power densities, spectral bandwidths, polarization of two excitation lasers, and atomic Doppler broadening on the total ionization yield and isotopic abundance are investigated numerically and the optimal excitation conditions for 176Yb enrichment are identified semi-quantitatively.