Origin of threshold electrons produced in decay of the Xe 4d−1 np resonance

Coincidence spectra of energetic electrons with threshold electrons were measured following photo-excitation of the Xe 4d_3/2, 5/2 → np resonances, in order to investigate the origin of threshold electrons, and the mechanism leading to formation of the Xe²⁺ 5p⁻² and 5s⁻¹5p⁻¹ final states. A two-step decay process was observed in the production of Xe²⁺ 5p⁻²(¹D) following decay of the 7p resonance, where the intermediate state is Xe^+* 5p⁻²(¹S)8p that autoionizes emitting a pseudo-threshold electron. This process was confirmed in a time-of-flight analysis of the coincidence spectra of the energetic electrons with the threshold photoelectrons. It is suggested that a similar two-step process also contributes to the population of excited Xe²⁺ states and is the main origin for the production of threshold electrons in decay of the 4d⁻¹ np resonances.     

A simple chiral Lagrangian approach toK→πππ decays andε′+0−

We analyse theK→πππ decays in the framework of a chiral Lagrangian supplemented by the 1/N expansion (N being the number of colors). The measuredK _L →π⁺π⁰π⁺ Dalitz plot is very well reproduced. Contrary to a recent claim, the Li-Wolfenstein relation between the CP impurities associated with theK→πππ(ε′_+0?) and theK→ππ(ε′) decay amplitudes is rather stable against isospin-breaking effects and higher-order (in the chiral expansion) weak operator corrections. We also predict a branching ratio of 2.1 10^?7 for the CP-conservingK _S →π⁺π⁰π⁺ decay.     

Theoretical study of the 3p-excitation in Mg+ and Mg0-inert gas collisions

Excitation of the 3p-states of Mg⁺ and Mg⁰ colliding with inert gases is treated within the coupled-channel impact parameter approximation. We have calculated the total excitation cross section and the linear polarisation of the (3p→3s)-emission as a function of the collision energy as well as the impact parameter dependence of the excitation probability and of the excitation amplitudes (expressed in terms of theλ, χ ^? parameters). Qualitative agreement with the experiments can be obtained when including both localised molecular orbital transitions at small internuclear distances (mechanism (i)) and the direct interaction between the Mg^+,0-valence electrons and the inert gas atom at large internuclear distances (mechanism (ii)). We present evidence that it is inadequate at impact energies below 1 keV to compute the phaseχ directly from the excitation amplitudes obtained in the coupled-channel impact parameter approximation.     

M4,5N4,5N4,5 auger electron spectrum of Ba metal

The Al Kα excited M_4,5N_4,5N_4,5 Auger spectrum of Ba has been measured from the metallic sample evaporated on a Ag substrate. The spectrum has been decomposed into individual line components after the background subtraction. The decomposed spectrum has been compared with the theoretical spectrum calculated for the 4d^?2 final state configuration in the mixed coupling scheme applying jj-coupling for the initial state and intermediate coupling for the final state. The most prominent structure of the spectrum shows the two 4d-hole coupling, but the structure which is caused by the Auger transitions M_,45N_2,3V has also been observed. The screening of the core holes in Ba metal seems to be produced by (5d6s) electrons. The simple excited atom model HF-calculations give an Auger kinetic energy shift (metal-free atom) of 16.7 eV, which is comparable to the experimental value 14–18 eV.     

Observation of resonance recombination lines in electron excited auger spectra of Gd

Combined measurements of electron excited N_4,5 Auger spectra and photoelectron emission on clean and oxidized Gd lead to a distinction between Auger lines originating from 4d → continuum and 4d → 4? resonance excitations. Several Auger structures are identified as due to the direct recombination of 4d⁹4?⁸ states with the 4f and valence electrons. The shape of the most prominent Auger line for oxidized Gd agrees perfectly with the Fano profile of the 4? photoemission intensity.     

Electron energy-loss spectroscopy of UHV-cleaved NiO (100) surfaces

Electron energy-loss spectroscopy of ～ 200 eV electrons has been applied to the study of the electronic states of clean NiO (100) surfaces. Initial attempt has been made on the identification of observed peaks, and they are attributed to the one-electronic transitions (O^2-2p → Ni²⁺3d, 4s and 4p; Ni²⁺3d → 4p, 3p → 3d and 4s), and the collective excitations (bulk plasmons of O^2-2p, Ni²⁺3d electrons, and coupled 2p and 3d electrons).     

Nuclear excitation and prompt fission in muonic238U

A study of muonic²³⁸U has been performed in a combined (μ ^?,γ f) and (μ ^?,γγ) coincidence experiment to investigate the role of non-radiative transitions and their fission probabilities. An augmentation of the outer fission barrier ofΔE _b =(0.6±0.1) MeV due to the presence of the muon is deduced. A significant contribution to the prompt fission yield not only results from the (2p→1s) and (3d→1s) non-radiative transitions, but also from other radiationless transitions. Specifically, the measured fission probabilities of the transitions (2p→1s), (3d→1s), and (3p→1s) are (1.5±0.4)%, (5.7±1.7)%, and (5.3±1.9)%, respectively.     

Hyperfine-structure and isotope-shift measurements in the 6s 5d↔6p 5d transitions of Ba I in the far-red spectral region

Measurements of the hyperfine structures in the 6p5d ¹ D ₂,³ D ₁ and³ F _{2, 3, 4} states of¹³⁵Ba and¹³⁷Ba, and isotope-shifts in several far-red transitions between the 6s 5d and 6p 5d configurations, as well as the transition 6s ^{2 1} S ₀→6s6p ³ P ₁ at 7,911 Å have been performed using high-resolution laser spectroscopy on a collimated atomic beam of natural barium. An analysis of the magnetic-dipole interaction in the 6p 5d configuration using effective one- and two-body hyperfine operators is presented. In particular the contact interaction was studied with respect to the correlation between the two valence electrons. Effects of strong configuration interaction were found. From a King-plot analysis of the isotope shift term- andJ-dependence of the field shift have been evaluated for the transitions between the 6s 5d and 6p 5d configurations. Relativistic Hartree-Fock (RHF) calculations have been performed of electron densities at the nucleus for six different configurations in Ba I and Ba II. The RHF calculations reproduce the experimental King-plot slopes quite well, while the absolute values, of the changes in electron density at the nucleus for the studied transitions, are found to be 9% lower than the results derived from a muonic experiment.     

Interpretation of auger energy shifts of silicon in solid silicon compounds

Chemical shifts of Auger transitions and photoelectron binding energies of silicon have been measured and interpreted using the quasi-atomic approach. The Si KL_2,3L_2,3 and L_2,3V₁V₁ Auger transitions and the binding energies of Si 2p and of the valence electrons at the maximum of the density of states V₁ have been investigated in solid silicon and in the compounds SiC, Si₃N₄, SiO₂, Na₂SiF₆ and T₃Si (T = V, Cr, Mn, Fe, Co, Ni). The relaxation-energy shift ΔR^ea_S(2p, 2p) describing the polarization effect (final-state effect) has been evaluated by AES and XPS measurements. Furthermore, the extra-atomic relaxation energy R^ea_D(2p) of the 2p electrons has been determined experimentally for silicon atoms in differing environments. This allows estimation of the potential parameter V(2p) describing the potential effect (initial-state effect). In general R^ea_D(2p) was found to be more sensitive to changes in chemical bonding than V2p). The behaviour of the quasi-atomic Si V₁ electrons seems to be the converse.     

Analysis of the sequence of insulator-metal phase transitions at high pressure in systems with spin crossovers

Possible variants of the Mott-Hubbard phase transitions at high pressure in systems with spin crossovers are considered. Owing to the universal character of the dependence of the effective Hubbard parameter U _eff(d ⁿ ) on the average number of d electrons, which is determined by the presence of spin crossovers, cascades of insulator-metal-insulator phase transitions in systems with d ³, d ⁶, and d ⁸ configurations become possible. Moreover, the systems with d ⁶ configuration can exhibit transitions from a metal in the absence of external pressure to an insulator at high pressure.     

The electron energy loss spectrum of EuO(100)

Energy losses of 200 eV to 2 keV electrons reflected from a disordered EuO(100) crystal show a bulk plasmon loss consistent with just less than six “quasi free” electrons per EuO unit, and 5p → nd resonance losses above the 5p threshold. The ratio of intensity of the 4d¹⁰ 4fⁿ⁰ → 4d⁹ 4fⁿ⁺¹ “giant resonance” loss at 142 eV to the corresponding direct recombination feature varies with energy, while the direct recombination and related Auger channels show similar energy dependence.     

Experimentally determined transition probabilities of the systems 6p2→6p6d, 6p7s, 6p8s of neutral lead

Branching ratio measurements have been performed for all of the observed transitions from eight levels in neutral lead (6p²→6p6d, 6p²→ 6p7s, 6p²→6p8s) excited in a hollow cathode discharge in the 200–730 nm spectral range. From the relative emission intensity data, a set of absolute transition probabilities is derived for 28 lines, including lines for which transition probabilities have not been previously published. The absolute scales are obtained by averaging the measured lifetimes of the ³P⁰_1,2, ¹P_1⁰(6p7s), ³F^0_2,3, ³D^0_1,2(6p6d) levels.     

Tunneling of 6<Emphasis Type="Italic">s</Emphasis><Superscript><Emphasis Type="Italic">2</Emphasis></Superscript> electrons in PbO and Bi<Subscript>2</Subscript>O<Subscript>3</Subscript>: XANES spectroscopy and DFT calculations

The results of XANES spectroscopy and DFT calculations are evidence for the occurrence of anomalous 2p_2/3→6s_1/2 electronic transitions in lead(II) and bismuth(III) oxides. The observed transitions may be due to the tunneling of outer 6s² electrons.     

Complete breakdown of the one-electron picture of auger spectra of solids

The very broad M₄₅?N₂₃N₄₅ (3d^-1 → 4p^-14d^-1) Auger spectra for metals in the range Pd to Te arise from complete breakdown of the one-electron picture of the final state double vacancy due to 4p^-14d^-1 ? 4d^-3?f giant Coster-Kronig fluctuation and decay processes. This is an example of atomic-like effects giving rise to level shifts and broadening which are large in comparison with typical widths of d-bands in solids. The 4p^-14d^-1 two-hole spectral function can be approximated by a 4p^-1 single-hole spectral function perturbed by a static, sharp 4d^-1 hole. The resulting Auger line-shapes are different from single-hole 4p^-1 line-shapes from XPS and XES. Analogous effects also occur for double vacancies involving one or two 4s-holes.     

Korrelationseffekte in den Auger-Spektren von Edelgasen

The possibility of studying correlation effects through Auger electron spectrometry has been shown recently by Krause, Carlson and Moddeman in the case of theK Auger spectrum of neon. As a further example we have measured theM _4,5 Auger spectrum of krypton with high resolution. Correlation effects have been found via the strong deviations of relative intensities of Auger diagram lines (e.g.M _4,5 N ₁ N _2,3(¹ p ₁)) from theoretical values and via the occurence of double Auger transitions, where one electron is emitted and another is excited. A critical examination of high resolution Auger spectra of noble gases, which has been measured so far, has shown that several non diagram lines can be assigned to double Auger transitions of the above kind.     

Radiative constants in the spectra of ions of the krypton isoelectronic sequence

The probabilities of the 4p ⁶,4p ⁵5p→4p ⁵(4d+5s) radiative transitions and the radiative lifetimes of the 4p ⁵4d,4p ⁵5s, and 4p ⁵5p levels are calculated semiempirically for the RbII-MoVII isoelectronic sequence.     

Many-body effects in l2mm auger electron spectra of Ge(CH3)4 excited by Mg Kα X-rays

The Ge:L₂MM Auger electron spectra excited by Mg Kα X-rays from Ge(CH₃)₄ free molecules have been compared with the corresponding spectra excited by Al Kα X-rays. The Al Kα excited spectra have characteristic features of the diagram Auger transitions, because the excitation energy is far above the L₂ ionization threshold. The energy of Mg Kα photons is 1.21 eV below the Ge:L₂ ionization threshold and thus the Mg Kα excited L₂MM Auger electron spectra indicate many-body effects, post collision interaction (PCI) effects and spectator Auger satellite structures. The L₂M_4,5M_4,5 type spectrum displays both these features but the L₂M_2,3M_4,5 type spectrum has only a spectator Auger satellite structure, because the (3p⁻¹3d⁻¹nl) final state interferes with the (3s) hole state.     

A pole in the3 S 1 hyperon-nucleon scattering amplitudes

Analyzing the enhancement of the λp invariant mass at 2.129 GeV in the rectionK ^? d→π ^? Λp we conclude that there is a pole in the³ S ₁ hyperonnucleon scattering amplitudes at invariant mass squarev=(4.534?i×0.022) GeV².     

Calculation of X-ray and Auger transition rates, lifetimes, X-ray wavelengths, and fluorescence yields of variously ionized silicon atoms

X-ray and Auger transition rates, X-ray wavelengths, and fluorescence yields are calculated for variously ionized silicon atoms with configurations 1s2s^m2pⁿ, m=0-2, n=1-6. The calculation has been performed using the Hartree-Fock atomic model. Intermediate coupling and configuration interaction have been taken into account. The energies and widths are found to be strongly affected by configuration mixing. The results from the present calculation have been compared with those available in the literature. The theoretical K_α hypersatellite and satellite spectra fall into several well-separated regions, corresponding to each of the possible number of spectator electrons in the 2s and 2p shells. The dependence of radiative rates and fluorescence yields on the number of spectator electrons is also investigated.     

Resonant structure due to the 3p→3d transition in the photoionization of Ca+

Many-body perturbation theory has been used to calculate the resonance structure (3p→3d) into the photoionization (4s→kp) for ion Ca⁺. This resonance structure results from the interference between a photoionization process or a photoionization with excitation process and a resonant Auger process. The coupled equation method has been improved to calculate this interference by the summation of specific classes of diagrams of perturbation theory to infinite order. The resonance structure in the region of the 3p threshold is enhanced via a super-Coster–Kronig transition. The theoretical results are in good agreement with experiment.