Doubly-excited States Research Articles

A new class of strongly bound, doubly excited valence states of neutral van der Waals molecules: Mg(3pπ,3pπ 3P J)⋅Ar(3Σ)

The first of a new class of strongly bound, double excited valence states of neutral van der Waals molecules, Mg(3pπ,3pπ 3PJ)⋅Ar(3Σ−), has been characterized by R2PI (resonance two-photon ionization) spectroscopy via excitation of metastable Mg(3s3pπ 3PJ)⋅Ar(3Π0+,0−) states in a supersonic jet. The MgAr(3Σ−) state has a bond energy of ∼2900 cm−1, more than twice that of the MgAr+ ion.

Photoionization study doublubly-excited helium at ultra-high resolution

The doubly-excited states of He were studied at the 9.0.1 undulator beamline of the Advanced Light Source. Using a 925 lines/mm grating and entrance/exit slits as narrow as 2.5 μm, the (2p,3d) state could be observed with a total experimental width of 1.0 meV (FHWM), which corresponds to a resolving power of Efrsol|E/gDE = 64,000 at hv = 64.12 eV. With this substantially reproved resolution, we reinvestigated the photoionization spectrum of He up to the double-ionization threshold at ∼= 79 eeV. Some previously unobservable Rydberg states and Rydberg series were identified, and the results are compared with state-of-the-art atomic-structure calculations as well with the results of a systematic study performed recently at the SX700/II beamline at BESSY.

Resonance structure of the photoionization cross sections of the Kr atom in the energy region between single and double ionization thresholds

The photoionization cross sections of the 4s-main line and the corresponding satellite lines of the Kr atom are studied experimentally and theoretically in the near-threshold region. Our measurements have been made using the photon induced fluorescence spectroscopy technique. Many-electron correlations have been accounted for in the calculations. It was shown that the interference of the direct-ionization channel and the channel of the ionization through the decay of the intermediate doubly-excited states explains the experimentally observed complex resonant structure of the 4s-photoabsorption spectrum of the Kr atom.

Electric-field effects on the 2p2 3Pe and 3Po states of H- below the H(N=2) threshold

A theoretical investigation of static electric-field effects on the 2p2 3Pe state and the doubly-excited 3Po states below the H(N=2) threshold is carried out using the method of complex-coordinate rotation. Products of Slater orbitals are used to represent the two-electron wavefunctions, with lmax=8 employed for individual electrons. Block matrices with up to Lmax=4 (G-states) are used to investigate the convergence behaviours for the resonance parameters (resonance energy and width). When the external electric field is turned on, the Stark effect is observed for the M=+or-1 components of the two nearly-degenerate 2p2 3Pe and 2s3p 3Po (2) states. Results for electric-field effects on the lowest 2s2p 3Po(1) state are also given, as well as effects on the 2s3s 3Se(1) and 2s4s 3Se(2) states.

Electron continua from 3-60 keV Li+-Ne and Na+-Ne collisions

Electron spectra from the Li+-Ne and Na+-Ne collisions have been measured for collision energies from 3.5 to 60 keV, ejection angles of 20-160 degrees , and electron energies in the 5-150 eV range. In both systems the electron spectrum consists of a relatively large continuum superimposed by discrete lines arising from doubly-excited atomic states. For the Li+-Ne system the continuum part decreases exponentially with electron energy, with a slope inversely proportional to the collision velocity. The angular distribution is approximately symmetric in the centre-of-mass system. For the Na+-Ne system the behaviour is more complicated, in particular, the continuum part cannot be fitted with a single exponential. The results are discussed in terms of recent models developed for one-electron systems by Solov'ev, Ovchinnikov and collaborators, describing the ionization process in terms of superpromotions, with the electron continuum being parametrized in terms of characteristic properties related to avoided and so-called hidden crossings of the quasimolecule.

Doubly-Excited States in the Spectrum of Molecular Hydrogen

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTDoubly-Excited States in the Spectrum of Molecular HydrogenChris H. Greene and Byungduk YooCite this: J. Phys. Chem. 1995, 99, 6, 1711–1718Publication Date (Print):February 1, 1995Publication History Published online1 May 2002Published inissue 1 February 1995https://doi.org/10.1021/j100006a012RIGHTS & PERMISSIONSArticle Views185Altmetric-Citations20LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (903 KB) Get e-Alerts

Comparison of autoionization rates for 3 l3 l' states of two electron systems

Three different calculational methods (AUTOLSJ, MZ, MCDF) are used to obtain energy levels and autoionization rates for doubly-excited states 3 l3 l' of two electron systems (6⩽ Z⩽54). By ordering all the states by energy within each block of a given angular momentum J and parity, it is possible to compare the autoionization rates obtained by the three methods. A comparison of the calculations is presented for Z = 18 and 26 and shows rather good agreement between the different methods. The Z dependences of the autoionizations rates are presented for the 3 s3 s 1 S 0 state to show general trends. Using the AUTOLSJ and MZ methods, the energy levels for Z = 6 and 8 are presented and compared with experimental data and very accurate calculations using the methods of complex-rotation, close-coupling, B-spline, and Feshbach projection.

Natural expansions of CI wavefunctions and analysis of Coulomb correlations for He(2p2 3P)-like ions

Natural expansions are presented for energetically acceptable configuration-interaction (CI) wavefunctions for the He(2p23P)-like ions when 1<or=Z<or=4. The symmetry of the natural orbitals and their occupation numbers are contrasted with existing results for the 1s2 1S ground state. Moreover, results are given for Coulomb holes, partial holes and interparticle expectation values (r12n), where -2<or=n<or=+2. Comparisons are made with recently reported findings when the 2p23P states were described by 'benchmark' explicitly-correlated (EC) wavefunctions. The natural expansions of the CI functions allowed us to explore the origin and convergence of the effects of Coulomb correlation. In particular, the analysis also highlighted significant changes in the relative importance of angular and radial correlation for these doubly-excited states as Z was increased.

Photoionization of Kr near the 4s threshold. IV. Photoionization through the autoionization of doubly-excited states

For pt. III see A. Ehresmann et al., ibid., vol., 27, p.1489-96 (1994). The photoionization cross sections for the production of the Kr II 4s state and Kr II satellite states were studied in the 4s ionization threshold region. The interference of direct photoionization and ionization through the autoionization decay of doubly-excited states was considered. In the calculations of doubly-excited state energies, performed by a configuration interaction technique, the 4p spin-orbit interaction and the (Kr II core)-(excited electron) Coulomb interaction were included. The theoretical cross sections are in many cases in good agreement with the measured values. Strong resonant features in the satellite spectra with threshold energies greater than 30 eV are predicted.

Weak correlation effects in doubly-excited circular states of barium

In the presence of weak external fields, we have investigated doubly-excited Ba atoms with one valence electron in a Rydberg circular state (n1=21, l1=n1-1), oriented with respect to the fields ( mu 1=l1), and the other electron in one of the low-lying states n2l2j2=6p1/2,3/2, 6d3/2,5/2 or 7s1/2. A theoretical model, including the e-e Coulomb interaction, predicts weak correlation effects leading to an angular-momentum mixing of the circular state when the inner electron is excited to anisotropic core states j2> 1/2 . Taking advantage of the field-ionization detection technique sensitive to the structure of the outer orbital, we have found evidence of such mixing. The implications and the limits of the model have been checked.

Autoionization of the 5s-np resonances of atomic iodine

The I 5s25p5(2P32/) to I* 5s5p5(3P,1P)np (n>or=6) Rydberg series have been studied by photoelectron spectroscopy monitoring the partial I+ 5s2 5p4 1D2, 3P2 and 3P1.0 ionization cross sections. The spectra are dominated by a large number of asymmetrical window-like resonances which are difficult to unravel. A qualitative analysis based on a comparison with the 5s-np excitation spectrum of atomic Xe allows a tentative assignment of only the lower members (n=6,7) of the series converging onto the first I+ 5s15p5 3P threshold. A more quantitative interpretation of the complex spectra has been obtained by configuration interaction calculations performed in intermediate coupling showing strong correlation effects between the singly-excited I* 5s15p5np and the doubly-excited states, mainly I* 5s25p35dnp. The theoretical results corroborate the tentative assignments for the singly-excited states and allow some additional resonances to be assigned to the I* 5s25p35dnp satellite states.

Doubly-excited states for the Na2 molecule: application to the dynamics of the associative ionization reaction

In a recent paper, we have performed accurate model potential calculations for the adiabatic excited states of the Na2 molecule. In view of dynamical calculations we propose a method to extract doubly excited potential curves, singly excited Rydberg series, and electronic couplings. In contrast to the previous work, the diabatic curves are correctly matching the adiabatic curves at large internuclear distances, and the electronic interactions do vanish in the asymptotic region. The adequacy of scaling laws to extract reduced parameters relevant to MQDT treatment of molecular autoionization is discussed. These parameters are used to calculate cross-sections for the associative ionization reaction at thermal collision energies when fine structure splitting can be neglected. In the framework of a simple model for the treatment of the long range dynamical couplings, we show the strong influence of the initial preparation of the atoms, and of long range population transfers. In contrast to the usual interpretation of experimental data, we predict that at least four doubly excited states may contribute efficiently to the process. Nevertheless, we may reproduce the marked variation of the observed ion signal as a function of the polarization of the exciting light. This work is a step towards a full treatment of the associative ionization between two cold atoms.

Spin-induced autoionization of quasibound levels in Be I

Beam-foil lifetime measurements of doubly-excited states of beryllium are shown to indicate the competing effects of decay by radiation and autoionization. Levels of the 2p3p3P and 2p3d1,3D terms cannot autoionize through the Coulomb interaction, but do so through spin-orbit mixing with autoionizing levels of the same configurations. Hartree-Fock calculations give theoretical estimates for the lifetimes of these levels which agree qualitatively with the experiments, and which depend on the unresolved fine structure in the 3P and 3D terms. The experimental results pose a challenge for a full theoretical treatment.

Doubly-excited state resonances of the helium-like nitrogen ion N5+ near then=3 threshold of N6+

Excitation energies, eigenvectors, partial and total widths of the singlets1 P (−) and triplets3 P (−) autoionising levels of the helium-like nitrogen ion N5+ converging to then=3 excitation threshold of residual ion are calculated using the diagonalisation approximation in the LS coupling scheme. The analysis and comparison of our calculations with other theoretical calculations are done, and some conclusions are drawn about the diagonalisation approximation for the description of the problem of multichannel resonant photoionisation in heliumlike systems.

Radiative interference effects in the dielectronic-recombination process of an electron with hydrogenlike uranium.

We have investigated the radiative interference effects in the electron-recombination process on the groups of mutually overlapping double-excited states of a heliumlike multicharged ion. Numerical calculations for the cross section of dielectronic recombination with ${\mathrm{U}}^{91+}$ are presented. The relative magnitude of the effects is found to reach about 25%.

Trajectory study of post-collisional mixing of Rydberg states after double charge exchange

Results are presented of classical trajectory calculations for the problem of large-L generation due to post-collisional interaction after conversion of the double excited states of multicharged ions formed in double charge exchange. It is shown that the large-L states are produced by this interaction but that the simple model of this phenomenon, proposed by the author previously, appears to be too crude. It is shown that the influence of the inhomogeneity of the electric field of the residual ion on the distribution of final orbital angular momentum of the Rydberg electron is important. The results imply that the uniform distribution function of the parameter x=Lfin/nfin provides a reasonable approximation.

Magnetooptical investigation of the broad spin-allowed bands in the metal-metal-bonded complexes nonahalodimolybdate(3-), Mo2X93- (X = Cl, Br)

The broad spin-allowed bands observed between 16 000 and 25 000 cm in CsMoX (X = Cl, Br) have been investigated by low-temperature single-crystal absorption and MCD spectroscopy. Using the exchange-coupled pair model, it is shown that these bands can be assigned to singly-excited pair states which involve trigonal t → e single-ion excitation. Weaker, sharper features are also observed which are attributed to doubly-excited pair states arising from intraconfigurational transitions (spin-flips) within the t single-ion orbitals. The spectral features are successfully modeled as a function of the Racah B and C parameters, the splitting between the trigonal t and e single-ion orbitals, and the metal-metal π exchange interaction. From the analysis, the metal-metal π interaction in the bromide complex is shown to be weaker than that of the chloride complex. Spin-polarized, transition-state calculations using the SCF-Xα-SW method were carried out on CsMoCl. Although the spin-singlet σ(Mo) → σ*(Mo) transition is calculated around 21 000 cm and is electric-dipole allowed, the low intensity (ϵ < 130) in this region indicates that this transition lies to higher energy, above 27 000 cm.

Photoionization of Kr near the 4s threshold. I. Experiment and LS coupling theory

Absolute cross sections for the transitions of the Kr atom into the 4s1 and 4p4nl states of the Kr+ ion were measured in the 4s-electron threshold region by photon-induced fluorescence spectroscopy (PIFS). The cross sections for the transitions of the Kr atom into the 4s1 and 4p4nl states were also calculated, as well as the 4p4nln'l' doubly excited states, in the frame of LS-coupling many-body technique. The cross sections of the doubly-excited atomic states were used to illustrate the pronounced contributions of the latter to the photoionization process, evident from the measurements. The comparison of theory and experiment led to conclusions about the origin of the main features observed in the experiment.

Doubly excited Rydberg states of He I and Ba I

The Auger decay widths of doubly-excited Rydberg states of He I and Ba I have been calculated by the multi-configuration Hartree-Fock procedure. The configuration mixing is crucial in obtaining the correct widths, while the energies seem to be relatively less sensitive to mixing. The usual mixing procedure is often unstable for doubly excited states and careful selection of configurations is required. An improved procedure for selecting the states for mixing is formulated, which seems to stabilize the calculation of both the energies and widths, with small numbers of configurations which are mixed. We apply the recipe to a selected set of doubly excited states of He and Ba. The long standing discrepancies in the widths for the series 7sns, 7snd, 8sns, and 8snd of Ba I withn > 11 may be explained by this procedure, except for the 7snd series. The calculated widths for the 7snd series are larger than the experimental values by a factor of 10–20. The difficulties of treating the states with both electrons in higher Rydberg orbitals are discussed.

Energies of Sr states with excited valence shell

Singly- and doubly-excited Sr states emerging upon excitation of the valence shell have been investigated. Only states with low values of the principal quantum numbern of the valence electrons have been considered: 5s4d, 5s5p, 5p2, 4d2 and 4d5p. These states have been treated by a perturbation theory based on the Dirac equations with model potential, the valence electrons interaction being considered as a perturbation. The zero-order approximation accounts for the main contributing interactions including the strong core potential screening. The applied calculation method was previously developed for highly-excited Rydberg states but its application also for states with lown was proved to be suitable.