Final State Correlation Effects Research Articles

Relativistic and correlation effects in the photoionization dynamics of oganesson (Z=118) : Spin-orbit-interaction-activated interchannel coupling effects

High-$Z$ atoms are excellent laboratories to study the combination of relativistic and many-electron correlation effects in electronic structure and dynamics. In the present work, the relativistic-random-phase approximation at different levels of truncation is employed to explore the final-state correlation effects in the photoelectron dynamics of the heaviest known element in the Periodic Table: oganesson (Og) with $Z=118$. The focus of this work is to illustrate the relativistic effects resulting from coupling different photoionization channels arising from spin-orbit split subshells, termed the spin-orbit-interaction-activated interchannel coupling effect. Comparison with the photoelectron dynamics of Rn on a qualitative level is also carried out, since Og is a homologue of Rn. The photoelectron dynamics of $7p,7s$, and $6d$ subshells are investigated and differences between Og and Rn, due to enhanced relativistic effects, are investigated.

Many-body and anisotropy effects in x-ray absorption spectra of pristine and defective vanadium pentoxide

X-ray absorption spectra of vanadium pentoxide (${\mathrm{V}}_{2}{\mathrm{O}}_{5}$) at the vanadium $K$ and $L$ edges are studied with multiple scattering calculations and good agreement with experiment is obtained when the full-potential and multichannel extensions of multiple scattering theory are used. The spectral shapes are analyzed in terms of the local electronic structure at the vanadium sites and they reveal strong anisotropy and final-state correlation effects. The strong polarization dependence of the spectra is explained by the low-symmetry ligand field and vanadyl bonding. The effect of oxygen vacancies, the major intrinsic defect type of ${\mathrm{V}}_{2}{\mathrm{O}}_{5}$, is investigated. Clear spectral changes are found for vanadium atoms next to an oxygen vacancy, which may serve as a fingerprint of defects in electron energy loss spectroscopy.

Auger-photoelectron coincidence spectroscopy of SiO 2

The O K-LL spectrum from a SiO 2 surface was measured in coincidence with O 1s photoemission in SiO 2. The coincidence lineshapes are compared to the simultaneously obtained conventional Auger lineshapes and to model lineshapes. The low-energy tail of the O K-LL lineshape from SiO 2 is suppressed in the APECS spectrum due to discrimination against extrinsic loss and initial-state shake processes, but remaining intensity indicated significant contribution from final-state shake-up/off processes. The results also confirm that a low energy satellite to the O K-L 2,3L 2,3 Auger line that is eliminated in the coincidence spectrum, and a high-energy shoulder that is enhanced in the coincidence spectrum, arise from an initial-state shake process, and final-state correlation effects, respectively. The results demonstrate the viability of applying APECS to the study of other metal oxides via the anion.

Photon-induced localization and final-state correlation effects in optically absorbing materials

Two consequences of the absorption of light in optically absorbing materials that appear not to have been recognized previously are: (1) localization of the final electron and hole states involved in the absorption process into wave packets and (2) propagation of these wave packets with their respective group velocities. We demonstrate the existence of these phenomena by applying first-order time-dependent perturbation theory to a simple model that can be solved analytically even when correlations that are ordinarily discarded in the random phase approximation are retained. This approach provides a natural explanation of components in surface- and interface-optical spectra that are related to energy derivatives of the bulk dielectric function εb and apparent differences in nominally bulk critical point energies Eg and broadening parameters Γ depending on surface conditions.

Near-threshold double photoionization:

Double photoionization of the inert gas atom with residual ion in the state implies coherent population of and partial waves in the two-electron continuum. The final continuum states are governed by the system of coupled Schrödinger equations in hyperspherical coordinates. The general expressions for the double photoionization cross sections are derived with a special emphasis on the experimental geometries used in the current experiments. The dynamic equations are simplified within assumptions of the extended Wannier ridge model, i.e. by employing a semiclassical approximation for the motion over the hyperradius and restricting configuration space to the Wannier ridge (regions where both electrons are at equal distances from the atomic core). The resulting equations are solved numerically for the Kr atom. The initial state of the active electron pair is described by the Hartree - Fock function or by a correlated function obtained in the configuration interaction scheme. The role of various initial- and final-state correlation effects is analysed. The results are compared with the available experimental data.

Elastic and inelastic scattering of electrons from Ar and Cl.

We have carried out extensive calculations of elastic and inelastic scattering of electrons from neutral argon and chlorine. The elastic and excitation cross sections are determined from the R-matrix method, in which the effects of dipole polarizability are included through the use of polarization pseudostates within the close-coupling expansions. For elastic scattering, our cross sections for Ar are compared to a number of other calculations and measurements. This provides a measure of the reliability of similar calculations for Cl. Our calculations of excitation include only transitions to the metastable levels of these atoms, where polarization effects are found to be quite important. Finally, ionization cross sections for these atoms are determined using the distorted-wave approximation; here, final-state correlation effects are found to be large.

Electron momentum spectroscopy of cyclopropane

The complete valence shell electron separation energy spectra and momentum distributions are measured for cyclopropane (C3H6) by high momentum resolution electron momentum spectroscopy (EMS) at a total energy of 1500 eV. Many-body calculations of the separation energies and spectroscopic factors using Green function methods are carried out and compared with the experimental data. The measured momentum distributions are compared with those calculated in the plane wave impulse approximation (PWIA) formalism using the double zeta quality molecular wavefunction of Snyder and Basch (1972). The agreement between the measured momentum distributions and the PWIA-SCF orbital momentum distributions is, in general, fair, although for the outer valence 2e' and 1e" states the SCF wavefunction underestimates the density at low momentum. The inner valence 1e' and 1a1' orbitals are found to be split by final state correlation effects. The agreement between the measured and calculated spectroscopic factors and separation energies is quite good, although the measured separation energy spectra contain significant strength up to 40 eV, this strength being of 1e' and 1a1' origin. The controversy with respect to the assignment of the 1a2" and 2a1' valence orbitals is examined in detail with the present EMS results and third-order algebraic diagrammatic construction ADC(3) Green function calculations seemingly leading to a diametrically opposite conclusion.

Coherence and correlation in the anisotropy of Ne KL-LLL satellite Auger decay.

The energies, intensities, and angular anisotropies of the Ne KL-LLL satellite Auger lines have been studied by the multiconfiguration Dirac-Fock method. In addition to the initial- and final-state correlation effects we have studied the influence of the quantum beat effect on this Auger spectrum. Since the energy splitting of the Ne 1${\mathit{s}}^{\mathrm{\ensuremath{-}}1}$2${\mathit{p}}^{\mathrm{\ensuremath{-}}1}$ $^{3}$P multiplet is much smaller than the lifetime broadening, the coherent excitation of these initial states by the in time and space localized electromagnetic pulse of the projectile has a drastic effect on the angular distribution of Auger electrons. To analyze this coherence effect we have generalized the theory of the angular distribution of Auger electrons to the case of coherent excitation of partially overlapping initial states. The results of our calculations are in good overall agreement with experiment. However, for a quantitative study of the influence of the coherence and the initial spin state on the anisotropy of these Auger lines new measurements with lower error limits are necessary.

Study of the valence electronic structure of the diene class of compounds by electron momentum spectroscopy and Green function methods. I. 1,2-propadiene

The complete valence-shell electron separation-energy spectra and momentum distributions are measured for 1,2-propadiene by high momentum-resolution electron-momentum spectroscopy at a total energy of 1500 eV. Many-body calculations of the separation energies and spectroscopic factors using Green function methods are carried out and, for the binding energies, compared with the experimental data. The measured momentum distributions are compared with those calculated in the plane-wave impulse approximation (PWIA) formalism using two respective SCF orbital wavefunctions, the second of which includes d-functions in the basis set. The agreement between the measured momentum distributions and the PWIA-SCF orbital-momentum distributions is, in general, fair, although for the outermost orbitals the SCF wavefunctions underestimate the density at low momentum. The inner valence 1b2 and 1a1 orbitals are found to be severely split by final-state correlation effects.

Electron momentum spectroscopy of methylamine

The complete valence shell electron separation energy spectra and momentum distributions are measured for methylamine by high-resolution electron momentum spectroscopy at a total energy of 1500 eV. Many-body calculations of the separation energies and spectroscopic factors using Green's function methods are carried out and compared with the experimental data. The measured momentum distributions are compared with those calculated in the plane wave impulse approximation (PWIA) formalism using an SCF orbital wavefunction which we constructed from a basis set of states that consisted of (10s, 6p, 1d)/[5s, 3p, 1d] for the carbon and nitrogen atoms and (5s, 1p)/[3s, 1p] for each hydrogen atom. The agreement between the measured momentum distributions and the present PWIA-SCF orbital momentum distribution is, in general, fair, although for the outermost valence 7a′ state the SCF wavefunction underestimates the density at low momentum. The inner valence 4a′ and 3a′ orbitals are found to be severely split by the final state correlation effects. The agreement between the measured and calculated spectroscopic factors and separation energies is quite good, although the measured separation energy spectra contain significant strength up to 41 eV, this strength being mainly of 4a′ and 3a′ origin.

Electron momentum spectroscopy studies on ring compounds. I. Benzene

The complete valence shell electron separation energy spectra and momentum distributions are measured for benzene by electron momentum spectroscopy at a total energy of 1200 eV. The measured momentum distributions are compared with those calculated in the plane wave impulse approximation (PWIA) formalism using a (9s5p/4s1p) to (4s2p/2s1p) Gaussian basis set. The level of agreement between the measured momentum distributions and the PWIA-SCF orbital momentum distributions is, in general, surprisingly good, particularly given the restricted nature of the current SCF basis set. The inner valence 2e2g, 2e1u and 2a1g orbitals are severely split by final state correlation effects. The agreement between the measured and Green function many-body method calculated spectroscopic factors and separation energies is good, although the measured separation energy spectra contain significant strength up to 51 eV, this strength being mainly of 2e1u and 2a1g origin.

Relativistic multichannel calculation of the Ne KLL and Ar L2M2,3M2,3 Auger transition rates.

The multichannel multiconfiguration Dirac-Fock method has been used to study the Ne KLL and Ar ${\mathit{L}}_{2}$${\mathit{M}}_{2,3}$${\mathit{M}}_{2,3}$ Auger-electron transitions. Final-state correlation effects are accounted for by simultaneously including several ionic configurations and ionization channels in the calculation of the final-state many-electron wave functions. Our computational approach is based on scattering theory, which properly accounts for the incoming wave boundary condition. The line intensities from our test calculation for Ne KLL transitions are in good agreement with earlier theoretical results and with experiment. The interchannel coupling is stronger for the final states of the Ar ${\mathit{L}}_{2}$${\mathit{M}}_{2,3}$${\mathit{M}}_{2,3}$ transitions, but the net effect on the line intensities is somewhat smaller than that for Ne. Even the most extensive multichannel calculations are not fully able to reproduce the measured total rate and the ratio of $^{3}$${\mathit{P}}_{0,1,2}$ to $^{1}$${\mathit{D}}_{2}$ transition rates. The remaining discrepancy in the branching ratios of Auger lines is attributed to the omission of initial-state configuration interaction, whereas the discrepancy between the measured and calculated total rates is suggested to be mainly due to the neglect of relaxation. Our results indicate that, in analogy to outer-shell photoionization, the final-state interchannel interaction does not in general affect the strongest Auger lines very much when the kinetic energy of the Auger electrons exceeds about 200 eV.

Study of the valence electronic structure of ethyne by electron momentum spectroscopy and Green’s function methods

The complete valence shell electron separation energy spectra and momentum distributions are measured for ethyne by high resolution electron momentum spectroscopy at a total energy of 1500 eV. Many-body calculations of the separation energies and spectroscopic factors using Green’s function methods are carried out and compared with the data. The measured momentum distributions are compared with self-consistent-field (SCF) orbital wave functions, the SCF wave functions including d functions in the basis sets. The agreement between the measured momentum distributions and the SCF orbital momentum distributions is excellent. The inner valence 2σg orbital is found to be split severely by final state correlation effects. The agreement between the measured and calculated spectroscopic factors and separation energies is in general very good, although the measured separation energy spectra contain significant strength up to 50 eV, this strength being mainly of 2σg origin.

Absorptive effects in K+ Lambda photoproduction on nucleons and nuclei.

Incorporating final-state correlation effects, we have reinvestigated the ${\ensuremath{\gamma}}^{1}\mathrm{H}\ensuremath{\rightarrow}{K}^{+}\ensuremath{\Lambda}$ elementary process. Our model not only resolves the persisting trouble of the small $\mathrm{KN}\ensuremath{\Lambda}$ coupling constant, but also yields agreement with cross-section data at higher energies. Using our amplitudes, we calculate angular distributions for the reaction $^{16}\mathrm{O}(\ensuremath{\gamma}, {K}^{+})_{\ensuremath{\Lambda}}^{16}\mathrm{N}$. While the forward cross section increases with increasing energy, the total cross section is almost constant from ${E}_{\ensuremath{\gamma}}=1.2$ through 2 GeV, suggesting that rather low photon energies hold promise for exploration of hypernuclear excitations.

The breakdown of the one-electron picture in the ligand XPES of Mo2 (O2CH)4, Mo2 (O2CCH3)4, and Cr2 (O2CCH3)4

The C1s and O1s photoelectron spectra of gaseous Mo2(O2CH)4, Mo2(O2CCH3)4, and Cr2(O2CCH3)4 are reported. An intense satellite peak is associated with C1s ionization in Mo2(O2CH)4 and Mo2(O2CCH3)4, but is absent in the other spectra. These observations are interpreted using ab initio MO calculations, together with initial and final state correlation effects. The intense satellite is associated with the transition δ→Lpπ, where δ is a metal–metal bonding orbital and Lpπ is an orbital of the same symmetry localized on the ligand from which ionization has occurred.

Final state correlation effects on the auger transition rates of methane

The doubly ionized Auger final states of CH 4 and the corresponding states of of Ne atom are studied by semi-internal configuration interaction (Cl) calculations. Correlation redistributes dramatically the intensities between the Auger diagram states and gives rise to strong satellite peaks in the law-kinetic-energy part of the spectrum.

Final-state correlation effects in Auger line shapes: Application to SiO2

Final-state correlation effects in Auger line shapes are considered within the cluster linear combination of atomic orbitals-molecular orbitals-configuration interaction theory with a parametrized Hamiltonian. A model problem is solved analytically to elucidate the role of final-state hole-hole correlation and to understand the localization of the holes on rather small subclusters of the system. The relationship of the correlation effects to the relative magnitudes of the one-center hole-hole repulsion $u$ and the bandwidth $\ensuremath{\Gamma}$ has been previously reported; however, this previous work has been limited to metallic single element conductors. This work extends the theory to covalently bonded insulators (and possibly semiconductors) consisting of more than one element. Application of the theory is made to the O $\mathrm{KVV}$ and Si ${L}_{23}\mathrm{VV}$ Auger line shapes from Si${\mathrm{O}}_{2}$. A high-energy shoulder at 511 eV in the O $\mathrm{KVV}$ line shape is interpreted as arising directly from correlation effects. A peak at 50 eV in the Si ${L}_{23}\mathrm{VV}$ line shape, its intensity significantly underestimated by the previous theory, is now accounted for; a peak at 70 eV previously suggested to be a shake satellite is now indicated also to arise from correlation effects. Both line shapes reveal a density of states primarily localized on an ${\mathrm{Si}}_{2}$O subcluster. The magnitude of the hole-hole repulsion on the subcluster and between neighboring ${\mathrm{Si}}_{2}$O subclusters is empirically determined from the Auger line shapes to be \ensuremath{\sim} 11 and 4 eV, respectively. The oxygen $2p$ nonbonding bandwidth is estimated to be \ensuremath{\sim} 6 eV, but in light of other theoretical and experimental results, our result is believed to be 1-2 eV too large. Reasons for our overestimate are discussed.

Strong correlation effects in the ionisation of CS 2

The Hell photoelectron spectrum of CS 2 is presented. This spectrum is investigated by two different Green's function calculations. For the outer valence region the origin and assignment of satellite lines of significant intensity is clarified. Strong final state correlation effects are found for the inner valence region showing the so-called breakdown of single-particle picture of ionisation.

Interpretation of the photoelectron spectrum of N2O4

Many-body Green's function calculations on the ionization spectrum of N2O4 are presented. The ordering of the five ionization potentials below 15 eV is found to be 4ag, 3b2g, 1au(π), 1b1g(π), with increasing binding energy. This ordering differs from that obtained by the application of Koopmans' theorem. Above 15eV binding energy the molecular orbital picture of ionization ceases to be valid. Some of the lines between 15 and 21eV disintegrate because of final state correlation effects. Above 21 eV the intensity associated with each orbital is distributed over numerous lines, leading to a dense line structure extending from about 21 to about 44eV. The energies and spectral intensities of >2300 cationic states have been computed.