Dielectronic recombination rates for ions of the magnesium sequence—II

The dielectronic recombination (DR) rate coefficient α^DR is explicitly calculated for Ar, Fe and Mo target ions of the Mg isoelectronic sequence (12 electrons). The 2p transitions are dominant at high temperatures and are considered in detail with full LS coupling. This work extends our previous study in which both the 3s, Δn = 0 and 3s, Δn ≠ 0 transitions are considered. Scaling of α^DR with free-electron temperature is also discussed.     

Dielectronic recombination rate for the Be-sequence

The dielectronic recombination (DR) rate coefficient α^DR is explicitly calculated for the Mo, Fe, Ar, and Ox target ions of the Be-sequence with four electrons, in the isolated resonance approximation. This work extends the previous study of the Mo³⁸⁺ ions at 1.4, 2.8, and 5.6 keV electron temperatures. Both Δn≠0 and Δn = 0 transitions are considered in detail. The Δn≠0 contribution still dominates, but the Δn = 0 effect becomes quite large for heavy ions. An explicit LS coupling scheme is employed throughout for the dominant transitions calculated here, and contributions from many other intermediate states and cascade transitions are included by comparing the dominant contribution with the more complete Mo³⁸⁺ case and proportionately scaling their effect. Nonrelativistic Hartree-Fock wave functions are used in the evaluation of the Auger and radiative amplitudes, and the continuum wave functions are calculated using the Hartree-Fock direct potential and explicit nonlocal exchange potential. The scaling property of α^DR and its breakdown are examined, and an improved form of the phenomenological formula is proposed.     

A note on Δn ≠ 0 Stark transitions in hydrogenlike atoms

In a gaseous helium or hydrogen target slow muons or antiprotons are captured into orbits with a high principal quantum number (n = 15 to 50) to form (μ^? α)⁺ ions, (p α)⁺ ions, or (p p) atoms respectively. In the subsequent deexcitation process Stark mixing of the intermediary states plays an important role. The successful Mainz Cascade Model assumed Δn = 0 for the Stark transitions, although formally no such selection rule exists. This note examines the reasons why Δn ≠ 0 Stark transitions play only a negligible role in the deexcitation cascade.     

An assessment of the effective Gaunt factor approximation

Based on comparisons with recent theoretical data, it is shown that the effective Gaunt factor for Δn = 0 transitions in alkali-like ions is within 25% of unity in most cases and is a slowly varying function of energy. A more complex energy dependence is noted for some non-alkali-like spectra, and especially for Δn ≠ 0 excitations. A method for the approximation of important correlation effects in the target is discussed for transitions of the type ns²¹S-nsnp¹P⁰.     

Dielectronic recombination rate coefficients for Fe23+ ion

The dielectronic recombination rate coefficients are explicitly calculated for the Li-like ion Fe²³⁺, which recombines with the continuum electron to form Fe²²⁺. Both 1s²2s and 1s²2p initial states are treated for the temperature range 1～8 keV. The rate coefficients are obtained from a direct evaluation of the Auger and radiative transition probabilities which are calculated from nonrelativistic Hartree-Fock wave functions. The L-shell electron excitation with Δn≠0 is found to be the dominant transition, while the 2s→2p excitation with Δn = 0 contributes approx. 10–25% of the Δn≠0 value. The K-shell excitation effect is about 1～30% in the temperature range considered, and the cascade effect is estimated to be a reduction in the rate of about 14%.     

Term structure of 4d-electron configurations and calculated spectrum in Sn-isonuclear sequence

Theoretical calculations of term structure are carried out for the ground configurations 4d^w, of atomic ions in the Sn isonuclear sequence. Atomic computations are performed to give a detailed account of the transitions in Sn⁺⁶ to Sn⁺¹³ ions. The spectrum is calculated for the most important excited configurations 4p⁵ 4dⁿ⁺¹, 4dⁿ⁻¹ 4f¹, and 4dⁿ⁻¹ 5p¹ with respect to the ground configuration 4dⁿ, with n=8-1, respectively. The importance of 4p-4d, 4d-4f, and 4d-5p transitions is stressed, as well as the need for the configuration-interaction CI treatment of the Δn=0 transitions. In the region of importance for extreme ultraviolet (EUV) lithography around 13.4 nm, the strongest lines were expected to be 4dⁿ-4p⁵ 4dⁿ⁺¹ and 4dⁿ-4dⁿ⁻¹ 4f¹.     

Bestimmung der Lebensdauer des 3d 9 4s 4p 4 P 3/2-Terms im Cu I-Spektrum mit optischer Doppelresonanz

The lifetime of the 3d ⁹ 4s 4p ⁴ P _3/2 state of Cu has been determined with optical double resonance by observation of radiofrequency transitions ΔF=0, Δm _F =±1 between hfs-Zeeman levels of the stable odd isotopes. The result is τ(3d ⁹ 4s 4p ⁴ P _3/2, Cu)=3.18(16)·10^?7 sec.     

Transition energy and dipole oscillator strength of 1s23d-1s2 nf transitions for Sc18+ ion

The transition energies of the 1s²3d-1s² nf (4?n?9) transitions and fine structure splittings of 1s² nf (n?9) states for Sc¹⁸⁺ ion are calculated with the full-core plus correlation method. The quantum defect of 1s² nf series is determined by the single-channel quantum defect theory. The energies of any highly excited states with n?10 for this series can be reliably predicted using the quantum defect as function of energy. Three alternative forms of the dipole oscillator strengths for the 1s²3d-1s² nf (n?9) transitions of Sc¹⁸⁺ ion are calculated with the transition energies and wave functions obtained above. Combining the quantum defect theory with the discrete oscillator strengths, the discrete oscillator strengths for 1s²3d-1s² nf (n > 9) transitions and the oscillator strengths densities corresponding to the bound-free transitions are obtained.     

Inversion-rotation spectrum and spectroscopic parameters of 14ND3 in the ground state

The far-infrared spectrum of ¹⁴ND₃ has been recorded in the region between 30 and 220 cm^?1 at a resolution, before deconvolution, of approximately 0.004 cm^?1. ΔJ = +1, ΔK = 0, a ← s and s ← a inversion-rotation transitions have been measured and assigned up to J″ = 19. These transitions, the pure inversion-microwave transitions and ground-state combination differences from the analysis of the ν₂ and ν₄ bands have been fitted simultaneously to an inversion-rotational Hamiltonian which includes Δk = ±3 and Δk = ±6 interaction terms. The ground-state spectroscopic parameters obtained in this way reproduce the transition frequencies within the accuracy of the measurements.     

Two-photon spectroscopy of ytterbium

Two-photon laser spectra of the Yb vapor have been obtained. Transitions to highly excited 4f¹⁴ 6sns¹S₀ and 4f¹⁴ 6snd ¹D₂ states are seen in direct two-photon excitation. Hybrid resonances involving 4f¹⁴ 6s6p ¹P⁰₁ and 4f¹⁴ 5d6s ³D₂ intermediate states lead to transitions to 4f¹⁴ 6sns¹S₀, 4f¹⁴ 6snp ³P⁰_2,1 and 4f¹⁴ 6snd ¹D₂ levels.     

Transition energies, wavelengths, oscillator strengths and transition probabilities between 1s, 1sns and 1snp (2?n?9) states for He-like Silicon

Multiconfiguration Hartree-Fock calculations with Breit-Pauli relativistic corrections are reported for electric dipole transition (E1) energies, wavelengths, weighted oscillator strengths and transition probabilities between all of the 1s², 1sns and 1snp (2?n?9) states for He-like silicon. The results are found to compare very well with available other results except Δn=0 due to differences in the calculated excitation energies.     

Rydberg transition dipole matrix elements from sum frequency generation spectra

A new method for determination of relative dipole matrix elements for transitions between excited states is presented, using sum frequency generation spectroscopy. The method is based on measuring the frequency spacing of related extrema in the dispersion like shapes within the SFG-spectrum, caused by interference between resonant and nonresonant parts in the third order polarizability. It is applied to CdI with the generated frequency in the range of the principal series 5s¹S₀ → np¹P₁, n = 12–28. Values of the products μ_6snpμ_{np5 s} are presented obeying the n^1-3 law.     

Resonance conversion of gamma radiation in the radiative transitions between neutron resonances

The influence of the resonance conversion on the α-particle spectra in the reaction (n, α) in low-energy transitions between neutron resonances is discussed. Unusual α spectra from neutron resonances in the reaction ¹⁴⁷Sm(n, α)¹⁴⁴Nd are considered as an example of such influence. The calculation of resonance conversion coefficients was performed for the transitions from K shell in the free levels of P shell of Sm atom. The large effect of resonance in the radiative transitions for the nuclei and atomic electron shells is observed.     

Far infrared spectrum and spectroscopic constants of AsH3 in the ground state

The far ir spectrum of arsine, AsH₃, was recorded in the range 25–100 cm^?1 with a resolution of approximately 0.004 cm^?1. ΔJ = +1, ΔK = 0 rotational transitions were measured and assigned up to J″ = 12. These transitions, together with the presently available microwave and submillimeter-wave data and ground state combination differences, were analyzed on the basis of a rotational Hamiltonian which includes Δk = ±3 and Δk = ±6 interaction terms. The derived ground state molecular parameters reproduced the transition frequencies of both allowed and “perturbation allowed” transitions within the accuracy of the measurements. The equilibrium structure was determined for the AsH₃ molecule.     

Energy levels of ions of silver and rhodium isoelectronic sequences with <Emphasis Type="Italic">Z</Emphasis> < 86

The method of extrapolation of the parameter of a model potential for states of one electron (4f, 5s, 5p, 5d, 5f) above the core 1s ²2s ²2p ⁶3s ²3p ⁶3d ¹⁰4s ²4p ⁶4d ¹⁰ and one vacancy (4d ⁹) in the same core is applied to calculate the energy levels in the silver and rhodium isoelectronic sequences with the maximum nuclear charge Z = 86. The energy levels of Ag-and Rh-like ions were used for the calculation of the energies of resonance transitions to the ground state ¹ S ₀ in Pd-like ions. Good agreement between the theoretical and calculated energies of the resonance transitions in Pd-like ions indicates the reliability of the results obtained.     

Resonance-enhanced multiphoton ionization spectroscopy of CH3 and CD3. Two-photon absorption selection rules and rotational line strengths of the ν3- and ν4-active vibronic transitions

To explore the possibility of K-level resolved, 2+1 resonance-enhanced multiphoton ionization (REMPI) processes of the methyl radical, the two-photon absorption selection rules and rotational line strengths of the 3₀¹ and 4₀¹ vibronic bands of the transition (n=3 or 4) were reported. Stringent selection rules, which were imposed upon these two-photon transitions, are the initial K″=3p (p=0,1,2,…), ΔK=±2, ΔU=±3, and ΔN=0,±1,±2 (O, P, Q, R, and S branches). The previously assigned 2₂² vibronic band of the methyl radical should be studied by the REMPI with a better spectral resolution and analyzed by the newly derived two-photon absorption selection rules and rotational line strength formulas.     

Studies of EPR g factors of the isoelectronic 3d series Cr, Mn and Fe in SrTiO3 crystals

The g-shifts Δg(=g−g_s, where g_s≈2.0023 is the free-ion value) of the isoelectronic 3d³ series Cr³⁺, Mn⁴⁺ and Fe⁵⁺ in SrTiO₃ crystals are calculated from the high-order perturbation formula based on the cluster approach for 3d³ ion in cubic octahedral site. The formula includes not only the contribution from the crystal-field (CF) mechanism, but also that from the charge-transfer (CT) mechanism (which is omitted in the CF theory). From the calculations, it is found that the contribution Δg_CT from the CT mechanism in sign is contrary to the corresponding Δg_CF from the CF mechanism and the relative importance of CT mechanism (characterized by |Δg_CT/Δg_CF|) increases with the increasing valence state (and hence the atomic number) of 3d³ ion. The positive g-shift Δg of SrTiO₃:Fe⁵⁺ is due mainly to the contribution of CT mechanism. So, for the explanations of g factors of the high valence state 3dⁿ ions (e.g. Mn⁴⁺ and Fe⁵⁺) in crystals, the contributions from both CF and CT mechanisms should be taken into account.     

K-shell Auger rates for multiply-ionized atoms: I. Neon

Theoretical Auger rates for the various terms of electron configurations 1s¹2s²2pⁿ, 1s¹2s⁰2pⁿ and 1s¹2s¹2pⁿ to the final terms after the Auger transitions are presented. The calculations are performed with the Hartree-Fock-Slater model. These rates can be conveniently used in the analyses of Auger-electron spectra produced, in particular, by heavy-ion collisions with neon.     

3s- and 3p-core level excitations in 3d-transition metal oxides from electron-energy-loss spectroscopy

3s- and 3p-core level excitations for a large number of 3d-transition metal oxides, with a formal 3d occupation from 3d⁰ to 3d¹⁰, have been measured by electron energy loss spectroscopy in reflection geometry (REELS) with primary energies 200 eV≤E ₀≤1600 eV. Their intensities decrease systematically with the formal 3d-count, classifying them as transitions to empty 3d-states. The structure of the 3s excitations is analysed in detail and is compared to the 3s-XPS photoemission spectra of the samples. This 3s-REELS structure and its change with the 3d occupation can be explained by the assumption that the excitation arises mainly from a 3s²3dⁿ→3s¹3dⁿ⁺¹ quadrupole transition.     

X-ray spectroscopy of multiply-charged ions from laser plasmas

Original results are reported on the observation and identification of spectra of multiply-charged ions in the range of λ ≈ 1.5–15 Å, which corresponds to transitions with a range of principal quantum number n. The main part of the review consists of tables with about a thousand spectral lines, which have been mainly observed in laser-plasma radiation, as well as in the solar corona and other laboratory sources at an electron temperature T_e≈10⁷°K. The accuracy for the wavelengths (Δλ) is the following: Δλ is equal to ≈ 0.0005 Å for λ ≈ 2.5 Å and it is equal to ≈ 0.003 Å for λ ≈ 15 Å. The spectral lines are considered for the following transitions: 1-n type for [H]-like ions (Z = 11–16)and [He]-like ions (Z = 11–26); 2-n type for [Li]-like ions (Z = 19–26), [Be]-like ions (Z = 22–34) and [Ne]-like ions (Z = 26–42); 3-n type [Co]- and [Ni]-like ions (Z = 73). The line-list contains about four hundred wavelengths for multiply-charged iron L-ions (Fe(XVII)-Fe(XXIV)) and is presented with identification of some of the transitions. The wavelengths and intensities of satellites of the [H]-like ions and [He]-like ions, which are caused by transitions from the doubly-excited autoionization states 2l2l′ and 1s2l2L′ of [He]-like ions (Z = 11–16) and [Li]-like ions (Z = 11–26), respectively, are also considered.