Atomic negative ions are fragile quantum systems in which correlation among the valence electrons plays a very important role. For doubly excited states correlation becomes dominant. Photodetachment is the process where a negative ion absorbs a photon and as a consquence ejects the outermost electron. A new detection scheme has been developed. The residual atom of a photodetachment is state selectively ionised by resonance ionisation spectroscopy. Investigations of the photodetachment threshold of tellurium with neutral particle detection yielded an electron affinity of 1589618(5) m^-1. With state selective detection the Li(2p) photodetachment threshold was investigated and the electron affinity was determined to be 498490(17) m^-1. Resonance structure in the Li^- photodetachment cross section near the Li(3p) threshold has been investigated. According to an assisting calculation this structure is analogous to the symmetrically excited intrashell (_3{0}_3^+)^1P^o state in H^-. In He^- the three doubly excited states, 1s3s4s ^4S, 1s3p^2 ^4P and 1s3p4p ^4P were investigated. The energy positions of all these resonances [1s3s4s ^4S: E_0=(2386803.1+-4.2) m^-1, Gamma=160(16) m^-1; 1s3p^2 ^4P: E_0=2.4782(55)x10^6 m^-1, Gamma=40(3)x10^3 m^-1; 1s3p4p ^4P: E_0=2633297(40) m^-1, Gamma=492(35) m^-1] agree with a recent calculation. The width of the 1s3s4s ^4S resonance agrees with this calculation, but for the 1s3p^2 ^4P resonance there is a slight discrepancy and the 1s3p4p ^4P resonance is only half as broad as predicted.
We consider single ionization of lithium atom in collisions with $p$ and O$^{8+}$ projectiles. Doubly differential cross sections for ionization are calculated within a relativistic non-perturbative approach. Comparisons with the recent measurements and theoretical predictions are made.
Highly precise variational calculations of non-relativistic energies of the (2p^2)^3P^e state of Helium atom are presented.We get an upper bound energy E=-0.71050015565678 a.u.,the lowest yet obtained.
In this paper we report calculations of potential energy curves in the $1.2 a.u.\le R\le100 a.u.$ range at Multireference Configuration Interaction (MRCI) level for doubly excited states of the H$_2$ molecule. We have focused on the $Q_2$ states which lie between the second and third ionization thresholds of H$_2^+$ molecular ion, i.e., $^2Σ_u^+$ state in which lie the H(2l) + H(2l') dissociation channels. The MRCI approach allowed us to successfully identify for the first time the molecular state which dissociates into hydrogen atoms at 2s state. Further, Generalized Oscillator Strength as a …
Using perturbed relativistic coupled-cluster (PRCC) theory we compute the ground state electric dipole polarizability, $α$, of doubly ionized alkaline earth metal ions $\rm{Mg}^{2+}$, $\rm{Ca}^{2+}$, $\rm{Sr}^{2+}$, $\rm{Ba}^{2+}$ and $\rm{Ra}^{2+}$. In the present work we use the Dirac-Coulomb-Breit atomic Hamiltonian and we also include the Uehling potential, which is the leading order term in the vacuum polarization corrections. We examine the correction to the orbital energies arising from the Uehling potential in the self-consistent field calculations as well as perturbatively. Our result…
We discuss the dynamics of the two-photon resonant ionization of helium involving two autoionizing states in the presence of two-color laser fields. The first source is tuned around the transition from the ground state to the 2s2p 1Po autoionizing state, and the second couples the state 2s2p 1Po to the 2p2 1S autoionizing state. The laser coupling between the doubly excited states is shown to lead to modifications of the Beutler-Fano profile and the appearance of an Autler-Townes doublet. This double resonance effect between autoionizing states can be observed at moderate laser intensities eas…
Accurate calculations of phase lag associated with coherent control where an excited system decays into more than one product channel have recently been reported for atomic barium in PhysRevA.105.013113 (2022). The present study extends the calculations to make predictions of that observable for another alkaline earth atom, strontium, with a discussion of its spectrum and phase lag for energies between the $Sr^{+}$ $4d_{3/2}$ and $4d_{5/2}$ thresholds. We will explore the physics influenced by the electron correlations of strontium and the long-range Coulomb potential. The behavior of the phas…
The photoionization of a helium atom by short intense laser pulses is studied theoretically in the vicinity of the $2s2p\,^1P$ doubly-excited state with the intention to investigate the impact of the intensity and duration of the exciting pulse on the dynamics of the autoionization process. For that purpose, we solve numerically the corresponding time-dependent Schrödinger equation by applying the time-dependent restricted-active-space configuration-interaction method (TD-RASCI). The present numerical results clearly demonstrate that the Fano-interferences can be controlled by a single high-fr…
Strong-field manipulation of autoionizing states is a crucial aspect of electronic quantum control. Recent measurements of the attosecond transient absorption spectrum of helium dressed by a few-cycle visible pulse [Ott et al., arXiv:1205.0519[physics.atom-ph] ] provide evidence of novel ultrafast resonant phenomena, namely, two-photon Rabi oscillations between doubly-excited states and the inversion of Fano profiles. Here we present the results of accurate \emph{ab-initio} calculations that agree with these observations and in addition predict that (i) inversion of Fano profiles is actually p…
A spectral approach is used to evaluate energies and widths for a wide range of singlet and triplet resonance states of helium. Data for total angular momentum $L=1,...,4$ is presented for resonances up to below the 5th single ionization threshold. In addition the expectation value of $\cos(θ_{12})$ is given for the calculated resonances.
The author supposes a capability of transition doubly excited configurations of separate atoms to a superconducting state. The conditions of this transition are determined and the experiments for its detection are offered. The capability of join of superconducting atoms in a superconducting condensate is considered. The capability of spontaneous formation of similar condensates in atmospheres of the Earth and Sun is considered.
Large-scale relativistic configuration-interaction calculation of energy levels of core-excited states of lithium-like ions is presented. Quantum electrodynamic, nuclear recoil, and frequency-dependent Breit corrections are included in the calculation. The approach is consistently applied for calculating all $n=2$ core-excited states for all lithium-like ions starting from argon ($Z = 18$) and ending with krypton ($Z = 36$). The results obtained are supplemented with systematical estimations of calculation errors and omitted effects.
In a joint experimental and theoretical endeavour, photoionization of metastable C4+(1s 2s 3S1) ions via intermediate levels with hollow, double-K-vacancy configurations 2s2p, 2s3p, 2p3s, 2p3d, 2s4p, 2p4s and 2p4d has been investigated. High-resolution photon-ion merged-beams measurements were carried out with the resolving power reaching up to 25,000 which is sufficient to separate the leading fine-structure components of the 2s2p 3P term. Many-body perturbation theory was employed to determine level-to-level cross sections for K-shell excitation with subsequent autoionization. The resonance …
We show that the correlation dynamics in coherently excited doubly excited resonances of helium can be followed in real time by two-photon interferometry. This approach promises to map the evolution of the two-electron wave packet onto experimentally easily accessible non-coincident single electron spectra. We analyze the interferometric signal in terms of a semi-analytical model which is validated by a numerical solution of the time-dependent two-electron Schrödinger equation in its full dimensionality.
Effective Hamiltonians for doubly excited Heliums states based on approximate O(4) symmetry are revised. New quantum numbers for a 4D Harmonic Oscillator are assigned to Helium states with both electrons in the n=2 shell. An effective Hamiltonian operator is constructed and optimzed by means of non-linear least-square fits to the energy levels of the Helium isoelectronic series. The results are interpreted in terms of electron correlation and a possible unified description of two-electron atom intrashell states.
The projection method is used to demonstrate the existence of positron attachment to three doubly excited states of helium. The e^+He(2s^2 1Se), e^+He(3s^2 1Se), and the e^+He(2s2p 3Po) states have binding energies of 0.447eV, 0.256eV and 0.486eV respectively. These energies were computed with the stochastic variational method and the configuration interaction method. These states will exist as resonances in the e^+ + He continuum and the e^+He(2s^2 1Se) state could be detectable in the e^+ + He collision spectrum. A resonance width of 0.068eV was computed for the e^+He(2s^2 1Se), state by usi…
Large-scale relativistic configuration-interaction method combined with many-body perturbation theory is consistently applied to calculations of the energy levels of the ground and inner-L-shell excited states of berylliumlike ions in the range $10 \leq Z \leq 92$. The quantum electrodynamics, nuclear recoil, and frequency-dependent Breit corrections are taken into account. The obtained results are supplemented with the systematical estimation of the uncertainties.
The recombination of a free electron into a bound state of bare, heavy nucleus under simultaneous production of bound-electron--free-positron pair is studied within the framework of relativistic first--order perturbation theory. This process, denoted as "negative-continuum dielectronic recombination" leads to a formation of not only the ground but also the singly- and doubly-excited states of the residual helium-like ion. The contributions from such an excited--state capture to the total as well as angle-differential cross-sections are studied in detail. Calculations are performed for the reco…
Recent advance in calculations of energy levels of the 1s2$l$2$l^{\prime}$ core-excited states for ions along the Li isoelectronic sequence from carbon to uranium suggested that theoretical predictions for the 1s2$l$2$l^{\prime}$ transitions are significantly more precise than most of the experimental results available today and can thus be used for calibrating measured X-ray spectra. This suggestion is verified in the present work by comparison with benchmark experimental results. We present a critical compilation of all available experimental data on the energy levels of the 1s2$l$2$l^{\prim…
In this work, we study the quantum entanglement for doubly excited resonance states in helium by using highly correlated Hylleraas type functions to represent such states of the two-electron system. The doubly-excited resonance states are determined by calculation of density of resonance states under the framework of the stabilization method. The spatial (electron-electron orbital) entanglement measures for the low-lying doubly excited 2s2, 2s3s, and 2p2 1Se states are carried out. Once a resonance state wave function is obtained, the linear entropy and von Neumann entropy for such a state are…
The two-loop self-energy correction to the Lamb shift of hydrogen-like ions is calculated for the $1s$, $2s$, and $2p_{1/2}$ states and nuclear charge numbers $Z = 30$-$100$. The calculation is performed to all orders in the nuclear binding strength parameter $Zα$. As compared to previous calculations of this correction, numerical accuracy is improved by an order of magnitude and the region of the nuclear charges is extended. An analysis of the $Z$-dependence of the obtained results demonstrates their consistency with the known $Zα$-expansion coefficients.
Photoelectron spectroscopy of 3s3p doubly excited helium dressed with strong near-infrared laser fields
Nagoya University（名古屋大学）；RIKEN, SPring-8 Center（理化学研究所 SPring-8 中心）；Fu-Jen Catholic University（辅仁大学）；Japan Synchrotron Radiation Research Institute（日本同步辐射研究机构）；University of Toyama（富山大学）
A detailed analysis on the effect of spherical impenetrable confinement on the structural properties of two-electron ions in S-states have been done. The energy values of 1sns [n = 2-4] (3Se) states of helium-like ions (Z = 2-5) are estimated within the framework of Ritz variational method by using explicitly correlated Hylleraas-type basis sets. The correlated wave functions used here are consistent with the finite boundary conditions due to spherical confinement. A comparative study between the singlet and triplet states originating from a particular electronic configuration shows incidental…
Energy levels and fine-structure intervals of the $1s2l2l'$ core-excited states are calculated for ions along the Li isoelectronic sequence from argon to uranium. The calculation is performed by the relativistic configuration-interaction method adapted for treatment of autoionizing core-excited states. The calculational approach includes the relativistic treatment of the nuclear recoil effect, the leading QED shifts as delivered by the model QED operator, and the frequency dependence of the Breit interaction. The $1s2l2l'-1s^22l$ transition energies are obtained by combining the present result…
It is shown that one can stimulate, by using the present-day laboratory magnetic fields, transitions between the $lm$ sub-levels of fast $μHe^+$ ions formating in muon catalyzed fusion. Strong fields also cause the self-ionization from highly excited states of such muonic ions. Both effects are the consequence of the interaction of the bound muon with the oscillating field of the Stark term coupling the center-of-mass and muon motions of the $μHe^+$ ion due to the non-separability of the collective and internal variables in this system. The performed calculations show a possibility to drive th…
$g$ factor of the $2p_j$ excited states in lithium-like ions
St. Petersburg State University（圣彼得堡国立大学）；ITMO University（伊托莫大学）；Petersburg Nuclear Physics Institute named by B. P. Konstantinov of National Research Centre “Kurchatov Institute”（库尔恰托夫国家研究中心鲍·波·康斯坦丁诺夫彼得堡核物理研究所）
Energies of (2s2 2p5 3l3l') and (2s 2p6 3l3l') states for sodiumlike ions with Z =14--100 are evaluated to second order in relativistic many-body perturbation theory starting from a neonlike Dirac-Fock potential. Second-order Coulomb and Breit interactions are included. Correction for the frequency-dependence of the Breit interaction is taken into account in lowest order. The Lamb shift correction to energies is also included in lowest order. Intrinsic particle-particle-hole contributions to energies are found to be 20-30% of the sum of one- and two-body contributions. Comparisons are made wit…
Parity nonconservation (PNC) effect in recombination of a polarized electron with a heavy H-like ion in case of resonance with a doubly excited state of the corresponding He-like ion is studied. It is assumed that photons of the energy corresponding to the one-photon decay of the doubly excited state into the $2^1S_0$ or the $2^3P_0$ state are detected at a given angle with respect to the incident electron momentum. Calculations are performed for heliumlike thorium ($Z = 90$) and gadolinium ($Z = 64$), where the $2^1S_0$ and $2^3P_0$ levels are near to cross and, therefore, the PNC effect is s…
Experimental and theoretical results are presented for double, triple, and quadruple photoionization of Si$^+$ and Si$^{2+}$ ions and for double photoionization of Si$^{3+}$ ions by a single photon. The experiments employed the photon-ion merged-beams technique at a synchrotron light source. The experimental photon-energy range 1835--1900 eV comprises resonances associated with the excitation of a $1s$ electron to higher subshells and subsequent autoionization. Energies, widths, and strengths of these resonances are extracted from high-resolution photoionization measurements, and the core-hole…
Rates and line strengths are calculated for the 2s22p53l3l' - 2s22p63l'' and 2s2p63l3l' - 2s22p63l'' electric-dipole (E1) transitions in Na-like ions with nuclear charges ranging from Z = 14 to 100. Relativistic many-body perturbation theory (RMBPT), including the Breit interaction, is used to evaluate retarded E1 matrix elements in length and velocity forms. The calculations start from a 1s22s22p6 Dirac-Fock potential. First-order RMBPT is used to obtain intermediate coupling coefficients and second-order RMBPT is used to calculate transition matrix elements. A detailed discussion of the vari…
Charge exchange collisions between ultracold fermionic 6Li atoms and 40Ca+ ions are observed in the mK temperature range. The reaction product of the charge exchange collision is identified via mass spectrometry during which the motion of the ions is excited parametrically. The cross-sections of the charge exchange collisions between 6Li atoms in the ground state and 40Ca+ ions in the ground and metastable excited states are determined. Investigation of the inelastic collision characteristics in the atom-ion mixture is an important step toward ultracold chemistry based on ultracold atoms and i…
A relativistic many-body method is developed to calculate energy and transition rates for multipole transitions in many-electron ions. This method is based on relativistic many-body perturbation theory (RMBPT), agrees with MCDF calculations in lowest-order, includes all second-order correlation corrections and includes corrections from negative energy states. Reduced matrix elements, oscillator strengths, and transition rates are calculated for electric-multipole (dipole (E1), quadrupole (E2), and octupole (E3)) and magnetic-multipole (dipole (M1), quadrupole (M2), and octupole (M3)) transitio…
A critical review on excited states of negative ions has been given recently by Buckman and Clark (1994), in a major update of the review by Schulz (1973). However, for completeness we include a summary of some known (mainly low lying) excited states. We include a brief discussion and indicate some problematic points with additional references. The observation of resonances in gas phase atomic collisions is discussed in this context. Finally we mention some very nice new results concerning the observation of these resonant states in particle surface interactions and briefly discuss the role th…
The wavelengths and radiative transition probabilities for transitions 2lnl'-1snl", 2lnl'-1s2l", 1s2lnl'-1s^2.nl", 1s2lnl'-1s^2.2l", and the autoionization decay probabilities for doubly excited states 2lnl', 1s2lnl' were calculated in ions with atomic numbers Z=6-36 for n=2-10, l'=0-3. The calculations were carried out by means of the MZ code based on the Z-expansion method. Relativistic corrections were taken into account within the framework of the Breit operator. The main difference with previous calculations by MZ code consists in accounting for the first order corrections in powers of 1/…
The process of internal conversion from excited electronic states is investigated theoretically for the case of the vacuum-ultraviolet nuclear transition of $^{229}{\mathrm Th}$. Due to the very low transition energy, the $^{229}{\mathrm Th}$ nucleus offers the unique possibility to open the otherwise forbidden internal conversion nuclear decay channel for thorium ions via optical laser excitation of the electronic shell. We show that this feature can be exploited to investigate the isomeric state properties via observation of internal conversion from excited electronic configurations of ${\ma…
Using the photon-ion merged-beams technique at a synchrotron light source, we have measured relative cross sections for single and up to five-fold photoionization of Fe$^{2+}$ ions in the energy range 690--920 eV. This range contains thresholds and resonances associated with ionization and excitation of $2p$ and $2s$ electrons. Calculations were performed to simulate the total absorption spectra. The theoretical results show very good agreement with the experimental data, if overall energy shifts of up to 2.5 eV are applied to the calculated resonance positions and assumptions are made about t…
Interaction between Rydberg atoms can significantly modify Rydberg excitation dynamics. Under a resonant driving field the Rydberg-Rydberg interaction in high-lying states can induce shifts in the atomic resonance such that a secondary Rydberg excitation becomes unlikely leading to the Rydberg blockade effect. In a related effect, off-resonant coupling of light to Rydberg states of atoms contributes to the Rydberg anti-blockade effect where the Rydberg interaction creates a resonant condition that promotes a secondary excitation in a Rydberg atomic gas. Here, we study the light-matter interact…
We present systematic calculations of energy levels of the $1s^22l$ and $1s2l2l'$ states of ions along the lithium isoelectronic sequence from carbon till chlorine. The calculations are performed by using the relativistic-configuration-interaction method adapted to the treatment of autoionizing core-excited states. The relativistic energies are supplemented with the QED energy shifts calculated within the model QED operator approach. A systematic estimation of the theoretical uncertainties is performed for every electronic state and every nuclear charge. The results are in agreement with exist…
We present a method for generating cold neutral atoms via charge exchange reactions between trapped ions and Rydberg positronium. The high charge exchange reaction cross section leads to efficient neutralisation of the ions and since the positronium-ion mass ratio is small, the neutrals do not gain appreciable kinetic energy in the process. When the original ions are cold the reaction produces neutrals that can be trapped or further manipulated with electromagnetic fields. Because a wide range of species can be targeted we envisage that our scheme may enable experiments at low temperature that…
The analysis of correlation energy of the simplest first approximation of a variational method for the intrashell states of two-electron atoms is the purpose of the present work. This method allows to divide energy of atom on Coulomb and additional not - Coulomb correlation parts with very high accuracy. Thus all the Coulomb interaction completely is taken into account in calculation and not-Coulomb terms enter only in additional correlation energy. The general formula for energy of additional correlation interaction is obtained and the constant of this interaction is determined. The algorithm…
X-ray production differential cross sections induced by C and Si ions with energies from 1 MeV/u down to 0.25 MeV/u, produced by the CMAM 5 MV tandem accelerator, have been measured for thin targets of Ti, Fe, Zn, Nb, Ru and Ta in a direct way. X-rays have been detected by a fully characterized silicon drift diode and beam currents have been measured by a system of two Faraday cups. Measured cross sections agree in general with previously published results. The ECPSSR theory with the united atoms correction gives absolute values close to the experimental ones for all the studied elements excit…
Emission lines from highly-excited states (n >= 5) of H- and He-like ions have been detected in astrophysical sources and fusion plasmas. For such excited states, R-matrix or distorted wave calculations for electron-impact excitation are very limited, due to the large size of the atomic basis set needed to describe them. Calculations for n >= 6 are also not generally available. We study the behaviour of the electron-impact excitation collision strengths and effective collision strengths for the most important transitions used to model electron collision dominated astrophysical plasmas, solar, …
Metastable levels in rhodium-like ions with the ground configuration $4p^{6}4d^{9}$ and the excited configurations $4p^{6}4d^{8}4f$ and $4p^{5}4d^{10}$ are investigated. The {\sl ab initio} calculations of the level energies, radiative multipole transition probabilities are performed in a quasirelativistic Hartree-Fock approximation employing an extensive configuration interaction based on quasirelativistic transformed radial orbitals. A systematic trends in behavior of calculated radiative lifetimes of the metastable levels are studied for the ions from $Z=60$ to $Z=92$. The significance of t…
Energies of (3s2 3p6 3d9 4l4l'), (3s2 3p5 3d10 4l4l'), and (3s 3p6 3d10 4l4l') states for Cu-like ions with Z = 30 -100 are evaluated to second order in relativistic many-body perturbation theory (RMBPT) starting from a Ni-like Dirac-Fock potential. Second-order Coulomb and Breit-Coulomb interactions are included. Correction for the frequency-dependence of the Breit interaction is taken into account in lowest order. The Lamb shift correction to energies is also included in lowest order. Intrinsic particle-particle-hole contributions to energies are found to be 20-30% of the sum of one- and two…
The structure and photoexcitation dynamics of high lying doubly excited states of the strontium atom with high angular momenta are studied in the vicinity of the Sr$^+(N=5)$ threshold. The spectra recorded using resonant multiphoton isolated core excitation are analyzed with calculations based on configuration interaction with exterior complex scaling, which treats the correlated motion of the two valence electrons of Sr from first principles. The results are rationalized with a model based on multichannel quantum-defect theory and transition dipole moments calculated with a perturbative treat…
The most important processes for the creation of S12+ to S14+ ions excited states from the ground configurations of S9+ to S14+ ions in an electron cyclotron resonance ion source, leading to the emission of K X-ray lines, are studied. Theoretical values for inner-shell excitation and ionization cross sections, including double KL and triple KLL ionization, transition probabilities and energies for the deexcitation processes, are calculated in the framework of the multi-configuration Dirac-Fock method. With reasonable assumptions about the electron energy distribution, a theoretical K$α$ X-ray …
We use correlation potential and many-body perturbation theory techniques to calculate spin-independent and nuclear spin-dependent parts of the parity nonconserving amplitudes of the transitions between the $6s_{1/2}$ ground state and the $5d_{3/2}$ excited state of Ba$^+$ and Yb$^+$ and between the $7s_{1/2}$ ground state and the $6d_{3/2}$ excited state of Ra$^+$. The results are presented in a form convenient for extracting of the constants of nuclear-spin-dependent interaction (such as, e.g., anapole moment) from the measurements.
We investigate the parity nonconservation effect in the elastic scattering of polarized electrons on heavy He-like ions, being initially in the ground state. The enhancement of the parity violation is achieved by tuning the energy of the incident electron in resonance with quasidegenerate doubly-excited states of the corresponding Li-like ion. We consider two possible scenarios. In the first one we assume that the polarization of the scattered electron is measured, while in the second one it is not detected.
We describe a numerical method that simulates the interaction of the helium atom with sequences of femtosecond and attosecond light pulses. The method, which is based on the close-coupling expansion of the electronic configuration space in a B-spline bipolar spherical harmonic basis, can accurately reproduce the excitation and single ionization of the atom, within the electrostatic approximation. The time dependent Schrödinger equation is integrated with a sequence of second-order split-exponential unitary propagators. The asymptotic channel-, energy- and angularly-resolved photoelectron distr…
We discuss possible search for optical transitions in Sm13+ and Sm14+ using ab initio calculations of differential dynamic polarizability. We calculate dynamic polarizability for M1 transition between first and second excited states of Sm14+ . Transition amplitudes and energies within optical range for states that contribute to the polarizability of the mentioned transition are presented. Employing simple analytical formula for polarizability data in the vicinity of a resonance and assuming that several values of the polarizability for different laser frequencies will be measured one can find …
Iridium ions near $4f$-$5s$ level crossings are the leading candidates for a new type of atomic clocks with a high projected accuracy and a very high sensitivity to the temporal variation of the fine structure constant $α$. To identify spectra of these ions in experiment accurate calculations of the spectra and electromagnetic transition probabilities should be performed. Properties of the $4f$-core-excited states in Ir$^{16+}$, Ir$^{17+}$, and Ir$^{18+}$ ions are evaluated using relativistic many-body perturbation theory and Hartree-Fock-Relativistic method (COWAN code). We evaluate excitatio…
