Collective Auger Decay of 4d−2 Double Inner-Shell Vacancy in Xe

The detailed level-to-level single and double Auger decay rates of Kr 3d−1 hole states are investigated in the framework of the first and second perturbation theory implemented by distorted wave approximation with the balanced large-scale configuration interaction of the successive ions being taken into account. The branching ratios of cascade and direct double Auger decay to the total probability are predicted to be 16.5% and 16.1%, respectively, for Kr and 16.8% and 17.2% for Kr , resulting in total double branching ratios of 32.6% and 34.0% for the two levels of Kr 3d−1 hole. A comparison is made with the available experimental results on the branching ratio into triply charged ions and good agreement was found with the most recent published work. This work represents the first theoretical study to correctly explain the experimental measurements. The complete pathways were depicted by including the direct double Auger decay process. Compared with the Auger decay of Ar 2p−1, the fraction of the cascade double of Kr 3d−1 is dramatically enhanced yet that of direct double Auger processes is only slightly increased.

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.

We present an ab initio theoretical method to calculate the resonant Auger spectrum in the presence of ultrafast dissociation. The method is demonstrated by deriving the L-VV resonant Auger spectrum mediated by the 2p3/2-1σ* resonance in HCl, where the electronic Auger decay and nuclear dissociation occur on the same time scale. The Auger decay rates are calculated within the one-center approximation and are shown to vary significantly with the inter-nuclear distance. A quantum-mechanical description of dissociation is effectuated by propagating the corresponding Franck-Condon factors. The calculated profiles of Auger spectral lines resemble those of atomic Auger decay but here the characteristic tails extend towards lower electron kinetic energies, which reflect specific features of the potential energy curves. The presented method can describe the resonant Auger spectrum for an arbitrary speed of dissociation and simplifies to known approximations in the limiting cases.

X-ray absorption creates electron vacancies in the core shell. These highly excited states often relax by Auger decay-an autoionization process in which one valence electron fills the core hole and another valence electron is ejected into the ionization continuum. Despite the important role of Auger processes in many experimental settings, their first-principles modeling is challenging, even for small systems. The difficulty stems from the need to describe many-electron continuum (unbound) states, which cannot be tackled with standard quantum-chemistry methods. We present a novel approach to calculate Auger decay rates by combining Feshbach-Fano resonance theory with the equation-of-motion coupled-cluster single double (EOM-CCSD) framework. We use the core-valence separation scheme to define projectors into the bound (square-integrable) and unbound (continuum) subspaces of the full function space. The continuum many-body decay states are represented by products of an appropriate EOM-CCSD state and a free-electron state, described by a continuum orbital. The Auger rates are expressed in terms of reduced quantities, two-body Dyson amplitudes (objects analogous to the two-particle transition density matrix), contracted with two-electron bound-continuum integrals. Here, we consider two approximate treatments of the free electron: a plane wave and a Coulomb wave with an effective charge, which allow us to evaluate all requisite integrals analytically; however, the theory can be extended to incorporate a more sophisticated description of the continuum orbital.

Single and double Auger decay processes of Ar+ 2p −1 hole levels belonging to the configurations of 2p 53s 23p 5 and 2p 53s3p 6 are investigated in the framework of perturbation theory implemented by the distorted wave approximation. The single Auger decay channels and rates are determined and the predicted total rates can differ by more than an order of magnitude for the levels of 2p 53s 23p 5, yet they are very close for levels belonging to 2p 53s3p 6. By combining the double photoionization cross sections of the neutral species, our theoretical Auger spectra of the single Auger decay process nicely interpreted a recent experiment [S.M. Huttula et al., Phys. Rev. Lett. 110, 113002 (2013)]. A configuration averaged branching ratio of 6.5% and 7.3% are predicted for the direct double Auger decay to the total probability for 2p 53s 23p 5 and 2p 53s3p 6, respectively, which is smaller than that of Ar 2p −1 hole states.

Chapter 6 - Electronic Decay in Multiply Charged Polyatomic Systems

The emission of an Auger electron is the predominant relaxation mechanism of core-vacant states in molecules composed of light nuclei. In this non-radiative decay process, one valence electron fills the core vacancy, while a second valence electron is emitted into the ionization continuum. Because of this coupling to the continuum, core-vacant states represent electronic resonances that can be tackled with standard quantum-chemical methods only if they are approximated as bound states, meaning that Auger decay is neglected. Here, we present an approach to compute Auger decay rates of core-vacant states from coupled-cluster and equation-of-motion coupled-cluster wave functions combined with complex scaling of the Hamiltonian or, alternatively, complex-scaled basis functions. Through energy decomposition analysis, we illustrate how complex-scaled methods are capable of describing the coupling to the ionization continuum without the need to model the wave function of the Auger electron explicitly. In addition, we introduce in this work several approaches for the determination of partial decay widths and Auger branching ratios from complex-scaled coupled-cluster wave functions. We demonstrate the capabilities of our new approach by computations on core-ionized states of neon, water, dinitrogen, and benzene. Coupled-cluster and equation-of-motion coupled-cluster theory in the singles and doubles approximation both deliver excellent results for total decay widths, whereas we find partial widths more straightforward to evaluate with the former method.

Cross sections for the electron-impact excitation of the $n=2$ states of the heliumlike ions Fe xxv and Kr xxxv are calculated in the relativistic distorted-wave approximation. Both bound-core orbitals and continuum-scattering orbitals are calculated using the Dirac Hamiltonian. The most significant relativistic effects result from the spinorbit mixing of the $2 ^{3}P_{1}$ and $2 ^{1}P_{1}$ excited states. We compare our results with previous calculations based on a perturbation-theory treatment of relativistic effects.

A calculation based on a relativistic distorted-wave approximation has been carried out for the electron impact excitation of the , , and -states of magnesium and the and -states of zinc from their respective ground states. Differential cross sections, coherence and correlation parameters as well as the spin-polarization parameters were obtained at incident energies of 10, 20 and 40 eV, respectively. The results for magnesium are analysed and compared with other available theoretical and experimental data while those for the zinc atom are reported for the first time.

Resonance excitation process for Ni-like gold

Based on a Multi-configuration Dirac-Fock method, a systematic study has been carried out for the decay processes of the inner-shell excited state 1s2s22S1,2of Li-like ions. It is found that only the Auger decay channel is dominant for the low Z ions, the two-electron one-photon radiative decay caused by a strong electron correlation becomes a competitive channel for the middle and high Z ions, whereas the magnetic quadruple radiative decay is also an important decay channel for the very heavy ions. At the same time, it is noticed that the Breit interaction can give a very important contribution to the Auger decay rate of the heavy ions.

On the basis of a multiconfiguration Dirac–Fock method, a systematic study has been carried out for the decay process of the 1s2s2 2S1/2 state of Li-like ions. It is found that the decay properties of these states are quite different along the isoelectronic sequence: for low-Z ions up to Z = 30, the Auger decay channel is dominant; for medium-Z ions up to Z = 80, a two-electron one-photon radiative decay caused by a strong electron correlation becomes a competitive channel; and for very heavy ions about Z = 90, the magnetic dipole radiative decay becomes important too. In addition, the QED contributions to the excitation energy and the contributions from the Breit interaction to the Auger decay rates are stressed for heavy ions in particular.

Theoretical study on decay processes of the core-excited states in BII

The normal Auger electron spectrum of the O2 molecule is assigned in detail on the basis of ab initio valence configuration interaction (CI) wavefunctions. Potential energy curves of the ground state, the core-ionized states and the doubly charged final states are calculated and Auger decay rates are obtained with the one-centre approximation. Using the lifetime vibrational interference method, band shapes are obtained for all contributions to the Auger spectrum. The calculated Auger electron spectrum allows us to identify all features observed experimentally. Significant differences to previous assignments are reported. A quantitative simulation of the spectrum is given on the basis of a curve-fitting procedure, in which the energetic positions and intensities of the theoretical bands were optimized. Besides providing a basis for a refined analysis of the spectrum, the fit allows us to assess the accuracy of the calculation. As expected for this level of theory, the absolute accuracy of the valence CI energies is found to be about 0.3 eV. The inherent error of the one-centre transition rates is less than 5% of the most intense transition in the spectrum. The frequently questioned one-centre Auger transition rates are shown to be rather appropriate if applied with reasonable wavefunctions and if the vibrational band structure of the molecular spectrum is properly taken into account.

Single-electron (SC) and double-electron capture (DC) in collisions of metastable ${\mathrm{Ar}}^{8+}$ ions with ${\mathrm{H}}_{2}$ have been studied by using X-VUV and Auger spectroscopy at 10 keV per charge. SC by the long-lived metastable ion ${\mathrm{Ar}}^{8+}{(2p}^{5}{3s)}^{3}{P}_{0.2}$ mostly populates inner-shell excited Na-like ${\mathrm{Ar}}^{7+**}[{(2p}^{5}{3s)}^{3}P,nl{]}^{2.4}{L}_{j}$ levels with $n=5,$ a small fraction going to $n=4.$ With the use of radiative and Auger decay rates, the observed X-VUV and Auger spectra are analyzed and compared with the spectra obtained by other authors. It is shown that the stabilization of these core-excited states is both radiative and autoionizing. DC by the metastable projectile reveals the formation of triply excited ${\mathrm{Ar}}^{6+***}$ ions. They stabilize along two Auger decay steps: the first one gives a low-energy electron, associated with the decay to the intermediate continua ${\mathrm{Ar}}^{7+}{(2p}^{5}{3l3l}^{\ensuremath{'}}),$ while the second step---originating from these ${\mathrm{Ar}}^{7+}{(2p}^{5}{3l3l}^{\ensuremath{'}})$ levels---gives a higher-energy electron, characteristic of the decay to the only available continuum ${\mathrm{Ar}}^{8+}{(2p}^{6}{)}^{1}{S}_{0}.$