Oscillator Strengths Of Lines Research Articles

VUV-synchrotron absorption studies of N2 and CO at 900 K

Photoabsorption spectra of N2 and CO were recorded at 900K, using the vacuum-ultraviolet Fourier-transform spectrometer at the DESIRS beamline of synchrotron SOLEIL. These high-temperature and high-resolution measurements allow for precise determination of line wavelengths, oscillator strengths, and predissociative line broadening of highly-excited rotational states with J up to about 50, and also vibrational hot bands. In CO, the perturbations of the A1Π-X1Σ+ vibrational bands (0,0) and (1,0) were studied, as well as the transitions to perturbing optically-forbidden states e3Σ-,d3Δ,D1Δ and a′3Σ+. In N2, we observed line shifts and broadening in several b1Πu-X1Σg+ bands due to unobserved forbidden states of 3Πu symmetry. The observed state interactions are deperturbed and, for N2, used to validate a coupled-channels model of the interacting electronic states. These data are appropriate for use in astrophysical or (exo-)planetary atmospheric applications where high temperatures are important and in future spectroscopic models of these molecules.

Astrophysical line diagnosis requires nonlinear dynamical atomic modeling.

Line intensities and oscillator strengths for the controversial 3C and 3D astrophysically relevant lines in neonlike Fe(16+) ions are calculated. A large-scale configuration-interaction calculation of oscillator strengths is performed with the inclusion of higher-order electron-correlation effects, suggesting that these contributions cannot explain existing discrepancies between theory and experiment. Then, we investigate nonlinear dynamical effects, showing that, for strong x-ray sources, the modeling of the spectral lines by a peak with an area proportional to the oscillator strength is not sufficient. The dynamical effects give a possible resolution of discrepancies of theory and experiment found by recent measurements, which motivates the use of light-matter interaction models also valid for strong light fields in the analysis and interpretation of astrophysical and laboratory spectra.

On the calculation of line strengths, oscillator strengths and lifetimes for very large principal quantum numbers in hydrogenic atoms and ions by the McLean–Watson formula

As a sequel to an earlier study (Hey 2009 J. Phys. B: At. Mol. Opt. Phys. 42 125701), we consider further the application of the line strength formula derived by Watson (2006 J. Phys. B: At. Mol. Opt. Phys. 39 L291) to transitions arising from states of very high principal quantum number in hydrogenic atoms and ions (Rydberg–Rydberg transitions, n > 1000). It is shown how apparent difficulties associated with the use of recurrence relations, derived (Hey 2006 J. Phys. B: At. Mol. Opt. Phys. 39 2641) by the ladder operator technique of Infeld and Hull (1951 Rev. Mod. Phys. 23 21), may be eliminated by a very simple numerical device, whereby this method may readily be applied up to n ≈ 10 000. Beyond this range, programming of the method may entail greater care and complexity. The use of the numerically efficient McLean–Watson formula for such cases is again illustrated by the determination of radiative lifetimes and comparison of present results with those from an asymptotic formula. The question of the influence on the results of the omission or inclusion of fine structure is considered by comparison with calculations based on the standard Condon–Shortley line strength formula. Interest in this work on the radial matrix elements for large n and n′ is related to measurements of radio recombination lines from tenuous space plasmas, e.g. Stepkin et al (2007 Mon. Not. R. Astron. Soc. 374 852), Bell et al (2011 Astrophys. Space Sci. 333 377), to the calculation of electron impact broadening parameters for such spectra (Watson 2006 J. Phys. B: At. Mol. Opt. Phys. 39 1889) and comparison with other theoretical methods (Peach 2014 Adv. Space Res. in press), to the modelling of physical processes in H II regions (Roshi et al 2012 Astrophys. J. 749 49), and the evaluation bound–bound transitions from states of high n during primordial cosmological recombination (Grin and Hirata 2010 Phys. Rev. D 81 083005, Ali-Haïmoud and Hirata 2010 Phys. Rev. D 82 063521, Ali-Haïmoud 2013 Phys. Rev. D 87 023526).

HIGH-RESOLUTION OSCILLATOR STRENGTH MEASUREMENTS OF THEv′ = 0,1 BANDS OF THEB-X,C-X, ANDE-XSYSTEMS IN FIVE ISOTOPOLOGUES OF CARBON MONOXIDE

We report oscillator strengths for six strong vibrational bands between 105.0 and 115.2 nm, associated with transitions from the v = 0 level of the X1Σ+ ground state to the v = 0 and 1 levels of the B1Σ+, C1Σ+, and E1Π states, in 12C16O, 12C17O, 12C18O, 13C16O, and 13C18O. These measurements extend the development of a comprehensive database of line positions, oscillator strengths, and linewidths of photodissociating transitions for all astrophysically relevant CO isotopologues. The E–X bands, in particular, play central roles in CO photodissociation and fractionation models of interstellar clouds and circumstellar disks including the early solar nebula. The resolving powers of the room-temperature measurements, R = 300,000–400,000, allow for the analysis of individual line strengths within bands; the measurements reveal J-dependences in the branch intensities of the C(v = 0,1)–X(0) and E(v = 0,1)–X(0) bands in all isotopologues. Minimal or no isotopologue dependence was found in the f-values of the C(v = 0,1)–X(0) and E(v = 0,1)–X(0) bands at a ∼5% uncertainty level. Revised dissociation branching ratios for the C(v = 0,1) and E(v = 0,1) levels are computed based on these f-values. The weak isotopologue dependence of the f-values presented here eliminates this mechanism as an explanation for the large 17O enrichments seen in recent laboratory photolysis experiments on CO at wavelengths from 105 to 108 nm.

ELECTRON IMPACT EXCITATION COLLISION STRENGTHS FOR EXTREME ULTRAVIOLET LINES OF Fe VII

Extensive calculations have been performed for electron impact excitation collision strengths and oscillator strengths for the Fe VII extreme ultraviolet lines of astrophysical importance. The collision strengths for fine-structure transitions are calculated in the B-spline Breit-Pauli R-matrix approach. The target wavefunctions have been calculated in the multiconfiguration Hartree-Fock method with term-dependent non-orthogonal orbitals. The close-coupling expansion includes 189 fine-structure levels of Fe VII belonging to terms of the ground 3p 63d 2 and excited 3p 53d 3, 3p 63d4l, 3p 63d5s, and 3p 63d5p configurations. The effective collision strengths are determined from the electron excitation collision strengths by integration over a Maxwellian distribution of electron velocities. The effective collision strengths are provided for 17766 fine-structure transitions at electron temperatures from 104 to 107 K. Our results normally agree with the previous R-matrix frame-transformation calculations by Witthoeft & Badnell. However, there are important differences for some transitions with the previous calculations. The corrections to the previous results are mainly due to more extensive expansions for the Fe VII target states.

The molecular structures and the relationships between the calculated molecular and observed bulk phase properties of phosphonium-based ionic liquids

Abstract The molecular and electronic structures of six ionic liquids (ILs) having the same cation (tetradecyl(trihexyl)phosphonium [P66614]), but with different anions, were obtained by quantum chemical calculations using density functional theory (DFT). Various molecular parameters were computed, including the inter-ionic H-bond length and angle, the energies of various molecular orbitals including HOMO and LUMO, the dipole moment (μ), the cation–anion interaction energy (∆E) and the electrostatic potential. The wavelengths and oscillator strengths of vibrational and electronic transition lines were also calculated and found to be in good agreement with measured IR and UV–vis absorption spectra. We have found strong correlations between the calculated quantum chemical parameters and the measured physical and chemical properties of the phosphonium ILs. In general, molar conductivity (Λ) increases, whereas viscosity decreases, exponentially with μ, and the melting point increases linearly with − ∆E.

INFRARED LABORATORY OSCILLATOR STRENGTHS OF Fe I IN THEH-BAND

We report experimental oscillator strengths for 28 infrared Fe I transitions, for which no previous experimental values exist. These transitions were selected to address an urgent need for oscillator strengths of lines in the H-band (between 1.4 um and 1.7 um) required for the analysis of spectra obtained from the Sloan Digital Sky Survey (SDSS-III) Apache Point Galactic Evolution Experiment (APOGEE). Upper limits have been placed on the oscillator strengths of an additional 7 transitions, predicted to be significant by published semi-empirical calculations, but not observed to be so.

Experimentally determined oscillator strengths in Rh II

This paper presents new experimentally determined branching fractions and oscillator strengths (log gf) for lines originating from 17 levels belonging to 5 terms of the first excited odd configuration 4d7(4D)5p in Rh II. The intensity calibrated spectra of Rh II have been recorded with a Fourier transform spectrometer between 25000 and 45000 cm−1 (2200–4000 Å). In this region, 49 lines have been identified and measured. By combining the branching fractions obtained from the spectra with previously measured lifetimes, log gf values are reported. The new results are compared with previous theoretical work.

Reinterpretation of the GaAsP far‐infrared spectra within the framework of the Verleur and Barker model of the alloy phonon spectra

AbstractIn this research, the model of five basic structural units (tetrahedra) proposed by Verleur and Barker [Phys. Rev. 149, 715 (1966)] (VB‐model) is completed by the statistical approach, which enables us to derive quantitative relations for the oscillator strengths of separate lines. The rule of proportionality of the oscillator strength sum to the content of the components for each dipole pair is developed as a criterion of random distribution of atoms in the lattice. Thus, a proper identification of observed lines was performed. It is shown that the optical‐reflection spectra obtained experimentally by the VB‐model authors for GaAsP solid solutions can be successfully explained using the VB‐model, without the hypothesis of clustering of binary GaAs as well as GaP tetrahedra, which they introduced.

Effects of the electron correlation and Breit and hyperfine interactions on the lifetime of the2p53sstates in neutral neon

In the framework of the multiconfiguration Dirac-Hartree-Fock method, we investigate the transition properties of four excited states in the $2p^53s$ configuration of neutral neon. The electron correlation effects are taken into account systematically by using the active space approach. The effect of higher-order correlation on fine structures is shown. We also study the influence of the Breit interaction and find that it reduces the oscillator strength of the $^3P^o_1 - ^1S_0$ transition by 17%. It turns out that the inclusion of the Breit interaction is essential even for such a light atomic system. Our ab initio calculated line strengths, oscillator strengths and transition rates are compared with other theoretical values and experimental measurements. Good agreement is found except for the $^3P^o_2 - ^1S_0$ M2 transition for which discrepancies of around 15% between theories and experiments remain. In addition, the impact of hyperfine interactions on the lifetimes of the $^3P^o_0$ and $^3P^o_2$ metastable states is investigated for the $^{21}$Ne isotope (I=3/2). We find that hyperfine interactions reduce the lifetimes drastically. For the $^3P^o_0$ state the lifetime is decreased by a factor of 630.

Magnetic dipole and electric quadrupole transitions in the trivalent lanthanide series: Calculated emission rates and oscillator strengths

Given growing interest in optical-frequency magnetic dipole transitions, we use intermediate coupling calculations to identify strong magnetic dipole emission lines that are well suited for experimental study. The energy levels for all trivalent lanthanide ions in the 4fn configuration are calculated using a detailed free ion Hamiltonian, including electrostatic and spin-orbit terms as well as two-body, three-body, spin-spin, spin-other-orbit, and electrostatically correlated spin-orbit interactions. These free ion energy levels and eigenstates are then used to calculate the oscillator strengths for all ground-state magnetic dipole absorption lines and the spontaneous emission rates for all magnetic dipole emission lines including transitions between excited states. A large number of strong magnetic dipole transitions are predicted throughout the visible and near-infrared spectrum, including many at longer wavelengths that would be ideal for experimental investigation of magnetic light-matter interactions with optical metamaterials and plasmonic antennas.

Dynamical correlation effects in the transition probability: A study for the atoms Li to Ar

Explicitly correlated wave functions constructed as a Jastrow correlation factor times a model function have been obtained for the ground and the first excited state of opposite parity of the atoms Li to Ar. Single and restricted multi-configuration model functions are employed. Line strength, oscillator strength and transition probabilities have been obtained. An analysis of the different correlation mechanisms considered, single particle excitations and dynamical correlations, on these quantities is carried out. All calculations have been done by using Variational Monte Carlo, except when no Jastrow is involved where calculations have been performed using the Optimized Effective Potential method.

Oscillator strengths for Be I

The electric dipole oscillator strengths for lines between some singlet and triplet levels have been calculated using the weakest bound electron potential model theory and the quantum defect orbital theory for Be I. In the calculations both multiplet and fine structure transitions are studied. We employed both the numerical Coulomb approximation method and numerical non-relativistic Hartree–Fock wavefunctions for expectation values of radii. The necessary energy values have been taken from experimental energy data in the literature. The calculated oscillator strengths have been compared with available theoretical results. A good agreement with the results in the literature has been obtained.

Uncertainty Analysis of Air Radiation for Lunar-Return Shock Layers

Uncertainty Analysis of Air Radiation for Lunar-Return Shock Layers

The energy levels and radiative transition probabilities for electric quadrupole and magnetic dipole transitions among the levels of the ground configuration, [Kr]4d104f4, of W24+

Large-scale multiconfiguration Hartree–Fock and Dirac–Fock calculations have been performed for the ground configuration, [Kr]4d104f4, energy levels of the W24+ ion. The relativistic corrections were taken into account in the quasirelativistic Breit–Pauli and fully relativistic Breit (taking into account QED effects) approximations. The role of correlation, relativistic, and QED corrections is discussed. Line strengths, oscillator strengths, and transition probabilities in the Coulomb and Babushkin gauges are presented for the electric quadrupole (E2) transitions among these levels. The magnetic dipole transitions are also investigated. Dependence of the E2 transition probabilities on the gauge condition of the electromagnetic field potential is studied as well.

Solar spectrum of silicon and diagnostics of the solar atmosphere

We review published papers dealing with the formation of the silicon solar spectrum and its application for the diagnostics of the solar atmosphere. We pay particular attention to studies on determination of the solar abundance of silicon, its reliable estimation being required for solving the problem of solar metallicity. We analyze the effect of the errors of the oscillator strengths of spectral lines, damping constants, and rates of inelastic collisions with hydrogen atoms on the silicon abundance estimation errors. We also summarize the studies devoted to the investigation of the effect of the deviation from the local thermodynamic equilibrium, inhomogeneous structure of the solar atmosphere, and small-scale magnetic fields on the Si I line formation.

Oscillator strengths for lines of astrophysical interest in Rh II

Aims. This work reports oscillator strengths for transitions of astrophysical interest in singly ionized rhodium. Methods. Seventeen radiative lifetimes in Rh + have been measured with the time-resolved laser-induced fluorescence technique and combined with theoretical branching fractions calculated using a relativistic Hartree-Fock model including core-polarization effects to obtain oscillator strengths. Results. On the basis of the good agreement between theory and experiment for the lifetimes, new reliable oscillator strengths have been deduced for a set of 113 Rh II transitions in the spectral range 153–418 nm.

ELECTRON EXCITATION COLLISION STRENGTHS FOR SINGLY IONIZED NITROGEN

Collision strengths for the astrophysically important lines in N II have been calculated in the close-coupling approximation using the B-spline Breit-Pauli R-matrix method. The multiconfiguration Hartree-Fock method with term-dependent non-orthogonal orbitals is employed for an accurate representation of the target wave functions. The close-coupling expansion includes 58 bound levels of N II. The 58 target levels belong to the terms of the ground 2s 22p 2 and singly excited 2s2p 3, 2s 22p3s, 2s 22p3p, 2s 22p3d, 2s 22p4s, 2s 22p4p, and 2s2p 23s configurations. The effective collision strengths are obtained by averaging the electron collision strengths over a Maxwellian distribution of velocities and these are tabulated for all 1653 fine-structure transitions among the 58 levels at electron temperatures in the range from 500 to 100,000 K. The line strengths, oscillator strengths, and transition probabilities for all E1 transitions are tabulated. The present results are compared with a variety of other close-coupling calculations. There is an overall good agreement with the 23-state calculation by Hudson & Bell in most part, but some significant differences are also noted for some transitions.

Oscillator strengths of allowed transitions for O III

The electric dipole oscillator strengths for lines in O III between some singlet and triplet levels have been calculated using the weakest bound electron potential model theory and the quantum defect orbital theory. In the calculations, both multiplet and fine-structure transitions are studied. The calculated oscillator strengths have been compared with available theoretical and experimental results. Good agreement with results in the literature has been obtained.

Transition probabilities and oscillator strengths of E1 transitions in Fe XII and Fe XIV

Non-orthogonal orbitals in the multiconfiguration Hartree–Fock approach are used to calculate line strengths, oscillator strengths and transition probabilities for E1 transitions among the fine-structure levels of the 3s 23p 3, 3s3p 4, 3s 23p 23d, 3s3p 33d, 3p 5 and 3s 23p3d 2 configurations in Fe XII and 3s 23p, 3s3p 2, 3s 23d, 3p 3, 3s3p3d, 3p 23d, 3s3d 2, 3p3d 2, 3s 24s, 3s 24p, 3s3p4s and 3s 24d configurations in Fe XIV. The lifetimes of excited levels belonging to these configurations of Fe XII and Fe XIV are also presented. An accurate representation of the levels has been obtained using spectroscopic and correlation radial functions. The wavefunctions exhibit large correlations and significant dependence of one-electron valence orbitals due to both the total and intermediate terms. The relativistic corrections are included through the one-body and two-body operators in the Breit–Pauli Hamiltonian. Progressively larger calculations are performed to check for important electron correlation contributions and for convergence of results. The atomic wavefunctions give excitation energies which are in close agreement with experiment. The present oscillator strengths and transition probabilities compare very well with previous large scale calculations.