Configuration Mixing Effects Research Articles

Exchange currents and configuration-mixing effects in the 16O(0 +)- 16N(0 −) transitions

In order to provide further information on the exchange currents in A 0 (the time component of the axial current), a detailed study is made of the 0 +-0 − transitions in A = 16: 16 N(0 −) → 16 O(0 +) + e − + \\ ̄ gn e and 16 N(0 +) + μ − → 16 N(0 −) + ν μ . Possible corrections to the usual treatment of the one-body processes are examined, such as the effects of higher-order terms in the Foldy-Wouthuysen transformation, the small component of the lepton wave function, and the difference in the radial behavior of the single-particle orbits. The interplay between exchange currents and configuration mixing is investigated at length. The relative importances of the soft-pion exchange currents A 0 soft and other exchange currents are evaluated to demonstrate the dominance of A 0 soft. The results of the present study support the conclusion obtained earlier that A 0 soft is important in explaining the experimental data on the 0 +-0 − transitions in A = 16.

Autoionization widths of doubly excited states for highly ionized systems: An application of the Stieltjes moment theory.

Processes such as dielectronic recombination or excitation-autoionization, which involve doubly excited states, are important for understanding the kinetics of laboratory plasmas. Theoretical studies of these processes require knowledge of Auger as well as radiative decay rates for the intermediate states involved. We have applied Stieltjes moment theory techniques to the problem of calculating autoionization widths for the (3l3l') doubly excited states of Kr/sup 25 +/ (sodiumlike krypton). Configuration-interaction wave functions were used to describe the resonances as well as the continuum. We have explored the effects of intermediate coupling, configuration mixing, and orbital relaxation on the calculated autoionization rates.

Surface alpha-clustering in the lead region

The effect of shell model configuration mixing on the reduced α-amplitude in heavy nuclei is investigated and discussed with respect to the question of α-clustering in nuclei. It is shown that extensive configuration mixing may enhance the α-amplitude under the Coulomb barrier by huge, largely arbitrary factors. In contrast to this the actual αclustering in the nuclear surface may well be described within the shell model including only relatively few configurations in the open shell.

Conjugation properties of double tensor operators and selection rules for their matrix elements

The application of parity, time, charge, hermitian and quasi-spin conjugations to the set of irreducible tensor operators separates two classes of tensor operators: polar and axial. Various product tensor operators, in particular one- and two-body double tensor operators, are subsequently examined as to their conjugation properties. As a result, new selection rules are found for their matrix elements which emphasize the need for a more precise labelling of tensorial ranks in order to account for the polar content and enable configuration mixing effects. The derived results are of particular importance to the form of phenomenological and equivalent Hamiltonians of atomic and molecular physics which are often presented as series of double tensor operators.

Quenching of the Gamow-Teller strength in the 42Ca(p,n) 42Sc reaction

Contributions to the Gamow-Teller strength in 42Ca(p,n) 42Sc reaction coming from second order configuration mixing effects are calculated. They account for half of the quenching presently unexplained from shell model calculations in the 0ℏ ω space. Other contributions which can provide further quenching are discussed.

Generation of cw 243 nm radiation and application to laser spectroscopy of the strontium isotopes

Intra-cavity second harmonic generation in a ring dye laser using lithium formate monohydrate has been observed to produce tunable cw UV radiation around 243 nm with single frequency powers of up to 1.4 mW. This wavelength region is of particular interest in the context of Doppler-free spectroscopy of atomic hydrogen. The radiation was used to excite an atomic beam of strontium to study the transition 5s 2 1S 0-4d5p 1P 1 of Sr I. The isotope shifts were determined as follows: 88Sr- 87Sr 123.7(8) MHz; 88Sr 285.0(8) MHz; 88Sr- 84Sr 600.1(9) MHz. The values are compared with results for other lines and muonic isotope shifts to obtain the specific mass shift and field shift in this transition and to study the configuration mixing effects. The hyperfine structure of 87Sr was not resolved, the intervals being very much less than the measured linewidth of 25 MHz.

Dielectronic-recombination rate coefficients for the lithium isoelectronic sequence

The dielectronic recombination (DR) rate coefficients are calculated in the nonoverlapping resonance approximation for the target ions ${\mathrm{O}}^{5+}$, ${\mathrm{Ar}}^{15+}$, ${\mathrm{Fe}}^{23+}$, and ${\mathrm{Mo}}^{39+}$ at several electron temperatures for the initial state $1{s}^{2}2s$. The autoionizing and radiative transition probabilities are computed with single-configuration, nonrelativistic Hartree-Fock wave functions and $\mathrm{LS}$ coupling. All possible Rydberg autoionizing states and their cascades are included. The relative contributions to the total DR rate of the $1s$, $2s(\ensuremath{\Delta}n\ensuremath{\ne}0)$, and $2s(\ensuremath{\Delta}n=0;2s\ensuremath{\rightarrow}2p)$ transitions are examined for each ion. We find that the main contribution to the DR rate is from $2s$-electron excitation (both $\ensuremath{\Delta}n\ensuremath{\ne}0$ and $\ensuremath{\Delta}n=0$ processes), although the contribution from $1s$ excitation is found to be as large as 40% of the total rate at high temperatures. Finally, the effect of configuration mixing is examined for a group of dominant states and the effect on the overall rate is estimated.

Inner shell excitation of lithium-like ions

view Abstract Citations (8) References (22) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Inner shell excitation of lithium-like ions Goett, S. J. ; Sampson, D. H. ; Clark, R. E. H. Abstract Collision strengths have been calculated for all fine-structure inner shell excitation transitions from the levels of the 1s2 2p and 1s2 2s configurations to the levels of the 1s2l2l' configurations in the Li-like ions Si XII, Ca XVIII, Fe XXIV, Kr XXXIV, and Gd LXII. The approach used is a Coulomb-Born exchange method that can be regarded as an application of first-order time-dependent perturbation theory, with the entire electrostatic interaction between the electrons plus the relativistic corrections included in the perturbation. The differences between this method and the one used by Sampson, Clark, and Parks (1979) are discussed. The results are presented, including configuration mixing, parentage mixing, and intermediate coupling effects. The results are in very good agreement with others obtained using more elaborate methods. Publication: The Astrophysical Journal Supplement Series Pub Date: January 1984 DOI: 10.1086/190921 Bibcode: 1984ApJS...54..115G Keywords: Atomic Excitations; Cosmic Plasma; Electron Transitions; Ionic Collisions; Lithium; Coulomb Collisions; Electron Impact; Space Plasmas; Tables (Data); Plasma Physics full text sources ADS |

Simultaneous analysis of magnetic moments and elastic magnetic electron scattering form factors

Analysis of the magnetic dipole moments and the elastic magnetic electron scattering form factors of the 1 2 + ground states of 19 F, 29 Si and 31 P demonstrates that the momentum transfer dependence of the data can be understood in terms of a q -independent M1 operator in combination with the effects of configuration mixing within the space of sd-shell orbits.

Collision strengths for inner-shell excitation of Li-like ions from levels of the 1 s22 s and 1 s22 p configurations to levels of the 1 s2 l2 l′ configurations

Coulomb-Born-Exchange data for collision strengths for inner-shell excitation from the levels of the 1s/sup 2/2s and 1s/sup 2/2p configurations to all fine-structure levels of the 1s2l2l' configurations in Li-like ions with 8< or =Z< or =74 have been fitted by simple functions of the impact electron energy epsilon in threshold units. To obtain collision rates, these functions can be readily integrated over a Maxwellian energy distribution for the electrons. Fits to the data for transitions between energy terms are also given. In addition, results are given for the transition energies and electric-dipole radiative line strengths. The basic collision-strength data to which the fits have been made are included for a sample of values for Z. These data cover the range of energies 1< or =epsilon< or =15 and include the effects of configuration mixing, parentage mixing, and intermediate coupling.

Hyperfine structure and isotope shift of high-lying metastable states of rhenium

Fourteen transitions in ReI, starting from high-lying metastable states belonging to the configurations (5d+6s)7, have been studied by laser-induced fluorescence in a collimated atomic beam, and accurate values for the isotope shifts in these transitions as well as for the hyperfine structure constants of 13 metastable and 9 excited states have been obtained. In addition, high precision measurements of the hyperfine structure of the states 5d5 6s24D7/2 and 5d6 6s6D1/2, 3/2, 5/2, 9/2 have been performed using the atomic beam magnetic resonance technique coupled with laser-induced state-selective detection of metastable atoms. The analysis of the hyperfine structure data yields experimental evidence for far configuration mixing effects on the off-diagonal spin-dipole matrix elements. The phenomenological interpretation of the isotope shifts shows the significance of off-diagonal field-shift effects.

Two-body current contribution toM1transitions and moments inCl38andK40

We deduce evidence for the existence of a two-body current contribution to $M1$ transitions and moments in nuclei, based on the application of shell model theory to experimental data. A complete specification of a two-body $M1$ operator, within a shell-model configuration, can be obtained by combining data from particle-particle and particle-hole nuclei. For this purpose, new particle-hole relations are derived for $M1$ transitions. The method of analysis is applied to the particle-hole pair $^{38}\mathrm{Cl}$-$^{40}\mathrm{K}$. The two-body current contributions could be effects of either configuration mixing, or mesonic currents, or both.

The effects of configuration mixing on excited charmonium decays

Configuration mixing betwenn ψ, ψ′ and ψ″ is considered in two models. In one model the confining potential consists of a scalar and a vector part; in the other model the vector confining potential interacts with a colour anomalous magnetic moment. It is shown that strong configuration mixing affects theEl transition rate and electronic decay widths of the vector mesons considerably.

Theoretical studies of photoexcitation and ionization in H2O

Theoretical studies are reported of the complete dipole excitation and ionization spectrum in H2O employing Franck–Condon and static-exchange approximations. Large Cartesian Gaussian basis sets are used to represent the required discrete and continuum electronic eigenfunctions at the ground-state equilibrium geometry, and previously devised moment-theory techniques are employed in constructing the continuum oscillator-strength densities from the calculated spectra. Detailed comparisons are made of the calculated excitation and ionization profiles with recent experimental photoabsorption studies and corresponding spectral assignments, electron impact–excitation cross sections, and dipole (e, 2e)/(e, e+ion) and synchrotron-radiation studies of partial-channel photoionization cross sections. The various calculated excitation series in the outer-valence (1b−11, 3a−11, 1b−12) region are found to include contributions from valence-like 2b2 (σ*) and 4a1 (γ*) virtual orbitals, as well as appropriate nsa1, npa1, nda1, npb1, npb2, ndb1, ndb2, and nda2 Rydberg states. Transition energies and intensities in the ∼7 to 19 eV interval obtained from the present studies are seen to be in excellent agreement with the measured photoabsorption cross section, and to provide a basis for detailed spectral assignments. The calculated (1b−11) X 2B1, (3a1−1)2A1, and (1b2−1)2B2 partial-channel cross sections are found to be largely atomic-like and dominated by 2p→kd components, although the 2b2(σ*) orbital gives rise to resonance-like contributions just above threshold in the 3a1→kb2 and 1b2 →kb2 channels. It is suggested that the latter transition couples with the underlying 1b1→kb1 channel, accounting for a prominent feature in the recent high-resolution synchrotron-radiation measurements. When this feature is taken into account, the calculations of the three outer-valence channels are in excellent accord with recent synchrotron-radiation and dipole (e, 2e) photoionization cross-sectional measurements. The calculated inner-valence (2a1−1) cross section is also in excellent agreement with corresponding measured values, although proper account must be taken of the appropriate final-state configuration-mixing effects that give rise to a modest failure of the Koopmans approximation, and to the observed broad PES band, in this case. Finally, the origins of the various spectral features present in the measured 1a1 oxygen K-edge electron energy-loss profile in H2O are seen to be clarified fully by the present calculations.

On the Effect of Configuration Mixing on the Radiation Spectrum Structure of Multicharged Ions

Satellite structure of the spectrum resulting from the consideration of configurations mixing was studied. These are the transitions of the type 1s2s22pn-1s22pn+1 and 1s2pn-1s22s22pn-3. Transition energies (eV) and probabilities (1013 s-1) were calculated for all possible values of "n". The perturbations theory by 1/Z was used in the calculations. Relativistic effects were taken into account within the frames of the Breit operator. The obtained numerical values of transition probabilities are averaged over J, J' (Tables I-IV) and then over LS, L'S' (Table V). Minimum and maximum energies of transition being studied are given for transition energies (E). Numerical results are presented for Mg, Al, Si ions.

Quark effects in nuclear physics

Since QCD is not well understood, we are forced to use phenomenological quark models fitted to known hadronic properties to learn about possible quark effects in nuclei and other multiquark systems. These “extrapolations” help us see how well the fundamental theory must be understood before we can obtain reasonable results. In this spirit, I discuss certain quark effects associated with valence quarks, sea quarks and valence antiquarks, using the M.I.T. bag model and potential models of quark dynamics. The contributions of valence quarks to many-nucleon forces turn out to be model-dependent, and not well understood. They contain large configuration-mixing effects which appear to arise from certain space-color-spin correlations. These correlations could sometimes cause an abnormal quark matter to collapse. The masses of multiquark states are also sensitive to the confinement mechanism. Sea-quark effects from q q fluctuations are shown to be important in nucleon properties. They also give rise to meson-nucleon coupling constants. The πNN result calculated from the M.I.T. bag model agrees with experiment, while the ρNN results are only roughly reproduced. Valence antiquark effects are discussed in the context of q 2 q 2 mesonic spectra. A cluster treatment using a nonrelativistic quark potential gives a detailed description of various rotational excitations of low L which cannot be obtained readily in other models.

Effects of configuration mixing on predominantlyf 7 2/n states inA=52?55 nuclei

Extensive shell-model calculations are performed onf7/2 nuclei withA=52–55. The model space includes the excitation of onef7/2 nucleon to thep3/2,f5/2 orp1/2 orbit. Spectra, electromagnetic properties (M1,E2,E4) andβ-decay are studied. It is found that almost all observables calculated in the enlarged space are in much better agreement with experiment than those of the simplef 7 2/n space.

Experimental evidence for far configuration mixing effects on off-diagonal hfs interaction between the (3d+4s) N+2 configurations of free atoms

In our systematic investigations on the hyperfine structure (hfs) of high lying metastable states in 3d-shell atoms we have found evidence for an extraordinary strong far configuration mixing effect on off-diagonal matrix elements between configurations. Using theABMR-LIRF method the hfs of (3d2 4s2)3P47Ti, (3d3 4s2)4P51V (3d5 4s2)4G55Mn and (3d6 4s2)3H57Fe has been measured. Values found for the effective radial parameters\(a^{k_s k_l } \) of the magnetic dipole interaction disagreed up to 300% with those known from hfs measurements of lower lying multiplets of the same configuration, even when intermediate coupling and electrostatically correlated second order hfs effects within each of the configurations are taken into account. We suggest that the main part of these discrepancies can be explained, if two-body core polarization is considered, which screens the ordinary one-body core polarization parametera3d10. Preliminary values for the corresponding parameters are given.

Excitation of high-spin unnatural parity states in 208Pb from the (p, p′) reaction at 135 MeV

Differential cross sections for the excitation of states at 6.42, 6.73 and 7.04 MeV in 208Pb by 135 MeV protons are reported. Both the excitation energies and the backward peaked angular distributions observed in this experiment and in a recent (e, e′) experiment strongly suggest that these states are predominantly one-particle-one-hole excitations with J π = 12 −, 14 − and 12 −, respectively. The present (p, p′) data are interpreted using a distorted wave impluse approximation and the effect of configuration mixing between the two 12 − states is investigated.

Intermediate coupling collision strengths for delta N = 0 transitions produced by electron impact on highly charged ions. I - Theoretical development and application to N = 2 levels in helium-like ions

view Abstract Citations (23) References (24) Co-Reads Similar Papers Volume Content Graphics Metrics Export Citation NASA/ADS Intermediate coupling strengths for DELTA n=0 transitions produced by electron impact on highly charged ions. I. Theoretical development and application to n=2 levels in helium-like ions. Sampson, D. H. ; Clark, R. E. H. Abstract A Coulomb-Born exchange method previously developed has been extended to transitions involving no change in principal quantum number n with intermediate coupling and configuration mixing effects included. The theory is used to calculate the collision and electric dipole line strengths for all fine-structure transitions with delta n = 0 and n = 2 in helium-like ions with nuclear charge number Z in the range between 6 and 74. This covers the entire range of Z of interest for astrophysical and controlled nuclear fusion applications; procedures are given for obtaining fits to the collision strength data using a simple form that is readily integrated over a Maxwellian energy distribution function to obtain collision rates. Publication: The Astrophysical Journal Supplement Series Pub Date: October 1980 DOI: 10.1086/190689 Bibcode: 1980ApJS...44..169S Keywords: Electron Impact; Electron Transitions; Fine Structure; Helium Ions; Ionic Collisions; Transition Probabilities; Astronomical Models; Atomic Energy Levels; Controlled Fusion; Electric Dipoles; Spectral Energy Distribution; Plasma Physics; Transition Probabilities full text sources ADS | Related Materials (1) Erratum: 1982ApJS...49Q.593S