Hollow States Research Articles

Coupling interface constructions of hollow Co-Mo mixed multiple oxidation states heterostructure for high-performance aprotic Li-O2 battery

Coupling interface constructions of hollow Co-Mo mixed multiple oxidation states heterostructure for high-performance aprotic Li-O2 battery

Production of C4+ (2s2p 3,1P) hollow states in collisions of 6-18 MeV C4+ (1s2, 1s2s 3S) mixed-state beams with gas targets

Normalized electron yields of the formation of 2s2p 3,1P states from the metastable states 1s2s 3,1S and from the ground state 1s21S were obtained in 6-18MeV C4+ collisions with H2, He, Ne and Ar gas targets. The method of zero-degree Auger projectile spectroscopy was used to detect electrons emitted in the Auger decay C4+ (2s2p 3,1P) → C5+ (1s) + e-with high resolution. These states are of particular importance in the detailed study of fundamental excitation mechanisms, i.e. electron-nucleus excitation, electron-electron excitation and electron-electron excitation with spin exchange. Currently, the role of the above mechanisms in the production of the 2s2p 3,1P states is investigated utilizing variable 1s2s 3S metastable fraction beams as a function of collision energy and target species. Our latest results are presented.

Auger decay and natural lifetime widths of single and double K-shell vacancy states of Al4+–Al11+ ions

The Auger decay of single and double K-shell hole and hollow states of Al4+–Al11+ was theoretically investigated in the framework of perturbation theory implemented by the distorted wave approximation. The natural lifetime widths of the hollow states x + are found to be 1.3–1.9 times larger than those of corresponding hole states x + . The maximal ratio is found originating from the hollow states of , which is ∼2.9 times as large as the hole states of . The calculated energy levels and natural lifetime widths are compared with the experimental and other theoretical results wherever available in the literature. The Auger decay rates and natural lifetime widths presented in this work are useful in the modeling of ultra-intensive x-ray laser interaction with aluminum.

Auger decay including direct double processes of K-shell hollow states of Ne+ and the related hypersatellite radiative transitions

In this study, we theoretically investigated single and double Auger decay processes from the K−2V (V = 3s, 3p, 3d, 4s, 4p, 4d) hollow states of Ne+ in the framework of the first- and second-order perturbation theory implemented by the distorted wave approximation. The direct double Auger decay rates were calculated based on the separation of knock-out and shake-off mechanisms. Atomic data, including the transition energy, single and double Auger decay rates and natural lifetime width, are obtained and compared with the experimental and theoretical results available in the literature. The natural lifetime widths of the K−2V hollow states, including the contributions from single and direct double Auger decay, are in excellent agreement with a recent experiment. Using our theoretical results, we diagnosed the relative population fractions of the initial quantum states prepared in the experiment and interpreted the measured Auger spectra. There is an excellent agreement between the theoretical and experimental results. Finally, the hypersatellite Kα radiative transitions relevant to these hollow states were investigated using the natural lifetime widths determined by single and direct double Auger rates.

The hollow university: Disaster capitalism befalls American higher education

Over the last 40 years, American institutions of higher education have been encouraged to align with the private sector by policymakers, think tank experts and businessmen in order to become more efficient and more accountable. In a wider sense, this new partnership may be evidence of what has been termed “disaster capitalism.” In disaster capitalism, crises are treated as economic opportunities. Governing bodies become “hollow states” which serve only to regulate contracts and provide further opportunities to entrepreneurs. The supposed crisis of accountability in American higher education may be such an opportunity. This paper argues for the emergence of the “hollow university” in American higher education. In the hollow university, state legislatures, think tank experts, leaders from the private sector and higher education administrators help to create a climate where institutions are more amendable to private sector partnerships. In order to determine this, I examine the desired inputs, processes, outputs and outcomes of four performance-based funding policies in the United States and demonstrate how the wording of these policies allow for and encourage private sector partnerships, specifically with emerging data companies such as Civitas Learning. Implications for the public mission of universities are discussed.

Traces in ion yields and electron spectra of the formation of Ar inner-shell hollow states by free-electron lasers

We explore the formation of Ar hollow states with two or three inner-shell holes by free-electron-laser radiation. We find that even-charged Ar ion states can be more populated than odd-charged Ar ion states. This depends on the pulse intensity and the number of energetically accessible inner-shell holes. Fully accounting for fine structure, we demonstrate that one-electron spectra bear the imprints of Ar hollow states with two inner-shell holes. Moreover, we show how the Auger spectra of these hollow states can be extracted from two-electron coincidence spectra.

Double−K−vacancystates in electron-impact single ionization of metastable two-electronN5+(1s2s3S1) ions

The role of hollow states intermediately produced in electron-impact ionization of metastable He-like $N{}^{5+}(1s2s{\phantom{\rule{0.16em}{0ex}}}^{3}{S}_{1})$ ions has been investigated in detail. A crossed-beam setup and suitable experimental techniques were employed for the measurement of accurate absolute cross sections and precise energy-scan data. Fine structures arising from $K$-shell excitations and associated resonances have been observed for this two-electron ion with less than $\ifmmode\pm\else\textpm\fi{}$0.5 eV uncertainty on the energy scale. Fine details, such as interference of the reaction pathways of direct ionization and excitation with capture of the incident electron followed by double-Auger decay, could be revealed. Ab initio calculations based on the convergent close coupling (CCC) approach are in good agreement with the experiment.

Understanding the nature and threats of drug trafficking to national and regional security in West Africa1

<p class="p1">Several West African states are threatened by increasingly powerful transnational organised criminal networks. Yet, scholarly work on the nature, characteristics and strength of these groups and how their activities threaten states remains sparse, leading to misunderstandings and inadequate appreciation of the precise nature of the threats they pose to West Africa. This paper seeks to fill these lacunae in our knowledge. It focuses on the nexus between drugs, crime and terrorism. It argues that, the financial spin-offs from criminal activities contribute to the development of opportunistic relationships between criminals and extremist groups that threatens West Africa’s fragile states. The analyses are based on evidence from several West African states, but employ the ongoing crisis in the Sahel, particularly Mali, as an empirical case, to demonstrate how ‘profitable collusion’ among different actors permits hollow states to become edifices that allows corruption, criminality and impunity to flourish.

Multiple ionization of argon under 123 eV FEL radiation and the creation of 3s-hollow ions

We present calculations on the multiple ionization of argon at the photon energy 123 eV and pulse duration 50 fs. At that photon energy, it is possible to drive the two-photon resonant Auger transition 2p → 4p, whose lifetime is 5.5 fs, much shorter than the pulse duration. The excitation of a 2p electron to the 4p state thus creates a hole which decays by an Auger process. We have also included above-threshold ionization from the outer shells of the neutral and singly ionized species, which becomes significant at intensities of the order of ∼1015 W cm−2 and higher. The populations of the various ionic species were obtained through the solution of the kinetic equations governing their production and decay during the pulse. The effect of the intensity distribution in the interaction volume has also been evaluated. We have further shown that doubly hollow ionic states of the type 3s03pn with 2 ⩽ n ⩽ 6 are created, which can decay only via spontaneous emission, with lifetimes orders of magnitude longer than the pulse duration. These hollow-ion states can potentially serve as a starting point for a variety of experimental investigations on doubly excited states.

Electron Correlation in the Formation of Hollow States along the Li-like Isoelectronic Sequence

Hollow-state (double K-shell vacancy) production in Li-like Be+, B2+, C3+, and F6+ ions colliding with He has been investigated using high-resolution Auger-electron spectroscopy. The formation of discrete states and their relative intensities show striking dependences on the nuclear charge Z of the ion. From the projectile velocity dependences of these states the contribution of the electron-electron interaction is determined, showing that the hollow states are formed largely by electron correlation with a strength that diminishes for increasing Z.

Studies on the hollow states of atomic lithium using a density functional approach

Density functional calculations are performed for 12 2l2l′nl″ (n ⩾ 2) triply excited hollow resonance series of Li, namely, 2s2ns 2Se, 2s2np 2Po, 2s2nd 2De, 2p2ns 2De, 4Pe, 2s2pns 4Po, 2s2pnp 4De, 2p2np 2Fo, 4Do, 2p2nd 2Ge, 4Fe and 2s2pnd 4Fo, covering a total of about 270 low-, moderately high- and high-lying states, with n as high as up to 25. The work-function-based exchange potential and the nonlinear gradient- plus Laplacian-included Lee–Yang–Parr correlation energy functional is used. The relevant Kohn–Sham-type equation is solved numerically using the generalized pseudospectral method offering non-uniform, optimal spatial discretization to obtain the orbitals and densities. The present single determinantal approach yields fairly accurate results for the nonrelativistic energies, excitation energies as well as the radial densities and other expectation values. Except for one state, the discrepancy in the calculated state energies remains well within 0.98%, whereas the excitation energies deviate by 0.02–0.58% compared to the available experimental and other theoretical results. Additionally companion calculations are made for the 37 3l3l′nl″ (n ⩾ 3) doubly hollow states (seven are n = 3 intrashell type) of Li with both K and L shells empty (up to n = 6) in the photon energy range 175.63–180.51 eV, with varying symmetries and multiplicities. Our calculation shows good agreement with the recent literature data for the only two such doubly hollow states reported so far, namely, 3s23p 2Po and 3s3p2 4Pe. The resonance series are found to be inextricably entangled with each other, leading to complicated behaviour in their positions. Many new states are reported here for the first time. This provides a simple, efficient and general scheme for the accurate calculation of these and other multiply excited Rydberg series of many-electron atomic systems within density functional theory.

Identification and characterization of the dielectronic process in the formation of twoK-shell vacancies in atomic Li by fast electron impact

Electron correlation effects in the production of two K-shell vacancies in lithium are investigated by bombarding atomic Li with 5-keV electrons. High-resolution Auger electron spectra show that discrete doubly vacant K-shell states are predominantly formed from ionization plus excitation, giving rise to the $2sns{}^{1,3}S$ and $2snp{}^{1,3}P$ states of ${\mathrm{Li}}^{+}.$ For these fast electron projectiles, the shake-up and dielectronic manifestations of the electron-electron interaction are shown to be the only mechanisms for creating the observed hollow states. The formation of the $2snp{}^{1,3}P$ states is found to be mediated only by the dielectronic process, permitting this aspect of the electron-electron interaction to be separately identified and its contribution characterized.

Differential electron scattering from positive ions measured by zero-degree ion–atom spectroscopy

Recent developments in quasi-free electron scattering from highly charged ions are reported. Results using a high-efficiency zero-degree Auger projectile spectroscopy setup are presented primarily for collisions of H- and He-like boron beams with H2 targets. A novel technique for the in situ control and determination of the metastable 1s2s3S beam fraction of He-like boron allowed for an accurate determination of absolute double differential scattering cross sections for 180° resonant and non-resonant electron scattering from both ground-(1s2) and mixed-(1s2, 1s2s3S) B3+ states. The observed richly structured B2+ (1s2lnl′) Rydberg series is produced by resonant excitation (RE) from the 1s2 ground state, while the triply excited B2+ (2s2l′2l′′) hollow ionic states are produced by RE from the 1s2s3S metastable state. The consistency of the method was checked by quasi-free electron scattering from H-like B4+ ions giving rise to the 2lnl′ Rydberg series. Differential R-matrix calculations within the electron scattering model for electron–ion scattering from both H-like and ground state He-like boron were found to be in excellent overall agreement. The production of triply excited (2s2l′2l′′) states by RE was also studied for the Z=5–9 isoelectronic sequence. These results convincingly demonstrate that large-angle differential scattering cross section measurements, practically impossible to perform with present day crossed or merged electron–ion beam techniques, are amenable to measurement through high resolution electron spectroscopy of ion–atom collisions, providing some of the most sensitive tests of atomic structure and electron–ion scattering calculations.

Symmetric rotor of lithiumlike hollow atoms

We present an explicit analytical construction of highly correlated triply excited hollow states in Coulombic three-electron systems. The construction is based on the simple idea that the three electrons will orient themselves in maximally polarized Stark states along three different axes with 120\ifmmode^\circ\else\textdegree\fi{} between them to minimize their mutual repulsion. This ansatz for the three-electron state, supplemented with an external rotational average and proper antisymmetrization, produces configuration-interaction mixing coefficients in good agreement with data obtained from ab initio calculations. Our ansatz leads to a simple and fairly accurate Z-scaling relation for energy splittings and dipole matrix elements along the lithium isoelectronic sequence. Despite our prediction of isomorphic correlation patterns and corresponding quasigood quantum numbers for L series of states, there is no numerical evidence that energies are well represented by rigid-rotor rotational spectra. We explain this by the explicit failure in multiply excited atoms of the nuclear and molecular physics theories of rotational structure.

Correlated electrons in lithiumlike hollow atoms.

We present a scheme for the explicit construction of highly correlated triply excited hollow states in Coulombic three-electron systems. Our analytical ansatz for the three-electron state is physically well justified and it produces configuration mixing coefficients in good agreement with data obtained from ab initio calculations.

Line shapesin photoexcitation of triply excited hollow states

Taking as the point of departure a frequently used experimentaldetection scheme, we present a derivation of the analyticalexpressions of the line shapes in partial decay channelspertaining to photoexcitation of triply excited hollow statesin atomic lithium with subsequent autoionization into a specificdoubly excited state in the singly charged ion. The line shapesrepresent useful generalizations of the Fano parametrizationof the profile of an autoionizing resonance. The line shapesgive the positions and widths of the triply excited autoionizingresonances, and carry information about specific partialautoionization widths, and partial asymmetry parameters. It isalso shown that a laser-induced transition from thetriply excited state to another lower-lying one can be usedto gain direct information about partial widths. The schemesare readily implemented experimentally, and would allow forthe first measurements of such quantities.

Simple analysis of correlation in few-body Coulomb systems: Application in the diffusion Monte Carlo method

An apporach is presented in order to study the interelectronic correlation in few-electron atomic or molecular systems. The main point is that the correlation is described as a mutual collision between all the electrons. This approach allows the determination of simple wave functions for complex systems including only three parameters, with a clear physical meaning. The method is applied to study three- and four-electron systems in different states, including the so-called hollow states for lithium and beryllium. The overall results are found to be in good agreement with those deduced using much more sophisticated wave functions. Subsequently, the present wave functions are chosen as trial wave functions in the diffusion Monte Carlo method. This approach leads to a very accurate determination of the ground-state energies of lithium, lithium negative ion, and beryllium atoms, indicating that it becomes possible to deduce with very good accuracy some properties of relatively complex systems with a quite simple wave function.

Double-K-Shell Vacancy Production in Li-Like C3+ Ions Colliding with Helium

The formation of doubly-vacant, i.e., “hollow”, states in 0.5–2.0 MeV/u Li-like C3+ ions colliding with helium has been investigated using high-resolution Auger electron spectroscopy. From the measured spectra, hollow two-electron states corresponding to 2l2l' configurations can be identified, as well as hollow three-electron states corresponding to 2l2l'2l'' configurations. The results suggest that the electron–electron interaction is important in producing the observed double-K-shell-vacancy states.

Hollow Atoms: a Theoretical Challenge

Hollow atoms are characterized by a large number of vacant inner shells and electrons occupying the outer shells. These “exotic” atomic species are formed in collision processes between highly-charged ions and several types of targets. The scope of the present contribution is to examine the decay properties of hollow atom states populated in collision with atoms, molecules, solid surfaces and clusters.

Photogeneration of Hollow Atoms: Recent Developments

Multiply-excited neutral atoms, or nearly neutral ions, with empty or only sparsely populated inner shells are termed “hollow atoms”. Hollow atoms can be created in a variety of ion collision experiments. An alternative method of generation is to use photo-excitation. The first photogeneration of hollow atom triply-excited states in neutral lithium was reported in 1994. The production of such triply-excited states is completely dependent on electron–electron correlations and their study has proved a challenge to both experimentalists and theorists. Results of recent experiments on hollow atoms carried out at synchrotron facilities in Europe, the USA and Japan are summarised and comparisons made with various theoretical predictions.