Determination Of Oscillator Strengths Research Articles

Determinations of transition probabilities and oscillator strengths of some levels in Eu I

Through combining experimental branching fractions (BFs) with radiative lifetimes, transition probabilities and oscillator strengths of Eu I for 39 lines from 16 excited levels were derived for the first time. The energies range from 27852.90 to 41443.70 cm-1. The BFs were determined in this work using the Fourier transform spectra available from National Solar Observatory database, and the lifetimes were obtained from literature. Furthermore, BFs for 22 lines, previously reported in the literature, were also determined for comparisons. The new results reported in this work will enrich spectral database and are expected to be widely used in many fields.

Absolute Quantification of sp3 Defects in Semiconducting Single-Wall Carbon Nanotubes by Raman Spectroscopy.

The functionalization of semiconducting single-wall carbon nanotubes (SWCNTs) with luminescent sp3 defects creates red-shifted emission features in the near-infrared and boosts their photoluminescence quantum yields (PLQYs). While multiple synthetic routes for the selective introduction of sp3 defects have been developed, a convenient metric to precisely quantify the number of defects on a SWCNT lattice is not available. Here, we present a direct and simple quantification protocol based on a linear correlation of the integrated Raman D/G+ signal ratios and defect densities as extracted from PLQY measurements. Corroborated by a statistical analysis of single-nanotube emission spectra at cryogenic temperature, this method enables the quantitative evaluation of sp3 defect densities in (6,5) SWCNTs with an error of ±3 defects per micrometer and the determination of oscillator strengths for different defect types. The developed protocol requires only standard Raman spectroscopy and is independent of the defect configuration, dispersion solvent, and nanotube length.

Determination of Dielectric Functions and Exciton Oscillator Strength of Two-Dimensional Hybrid Perovskites

Two-dimensional (2D) hybrid organic inorganic perovskite (HOIP) semiconductors have attracted widespread attention as a platform of next-generation optoelectronic devices benefiting from their natu...

Determination of oscillator strengths by using magic wavelengths of the 5s1/2 → 5p1/2,3/2 transitions for Rb

The energy levels and electric dipole matrix elements of Rb atom are calculated using the relativistic configuration interaction with core polarization method. These energy levels and matrix elements are further employed to calculate the electric dipole static and dynamic polarizabilities of the 5s1/2, 5p1/2 and 5p3/2 states. Finally, the magic wavelengths of the 5s1/2 → 5p1/2,3/2 transitions are obtained for linearly and circularly polarized light. We suggest that the accurate measurement on the magic wavelengths for circularly polarized light could be used to determine the high-precise oscillator strengths of the 5p1/2 → 5d3/2, 6d3/2, 7s1/2, 8s1/2 and 5p3/2 → 5d3/2, 5d5/2, 6d5/2, 7s1/2, 8s1/2 transitions.

Excitons without effective mass: Biased bilayer graphene

Understanding the dynamics of excitons in two dimensional semiconductors requires a theory that incorporates the essential physics distinct from their three-dimensional counterparts. In addition to the modified dielectric environment, single-particle states with strongly non-parabolic dispersion appear in many two-dimensional band structures, so that "effective mass" is ill-defined. Focusing on electrostatically-biased bilayer graphene as an example where quartic (and higher) dispersion terms are necessary, we present a semi-analytic theory used to investigate the properties of ground and excited excitonic states. This includes determination of relative oscillator strengths and magnetic moments (g-factors) which can be directly compared to recent experimental measurements.

Atomic Data Revisions for Transitions Relevant to Observations of Interstellar, Circumgalactic, and Intergalactic Matter

Abstract Measurements of element abundances in galaxies from astrophysical spectroscopy depend sensitively on the atomic data used. With the goal of making the latest atomic data accessible to the community, we present a compilation of selected atomic data for resonant absorption lines at wavelengths longward of 911.753 Å (the H i Lyman limit), for key heavy elements (heavier than atomic number 5) of astrophysical interest. In particular, we focus on the transitions of those ions that have been observed in the Milky Way interstellar medium (ISM), the circumgalactic medium (CGM) of the Milky Way and/or other galaxies, and the intergalactic medium (IGM). We provide wavelengths, oscillator strengths, associated accuracy grades, and references to the oscillator strength determinations. We also attempt to compare and assess the recent oscillator strength determinations. For about 22% of the lines that have updated oscillator strength values, the differences between the former values and the updated ones are ≳0.1 dex. Our compilation will be a useful resource for absorption line studies of the ISM, as well as studies of the CGM and IGM traced by sight lines to quasars and gamma-ray bursts. Studies (including those enabled by future generations of extremely large telescopes) of absorption by galaxies against the light of background galaxies will also benefit from our compilation.

On SH Molecules in Umbral Spectra

Following our predictions on detectability, very weak lines of the SH molecules have been reported as identified in the photospheric spectrum of the Sun. This could be the first detection of a mercapto radical in the solar spectrum, thus placing confidence in the solar abundance of Sulfur. The observations additionally tested the utilized theoretical band oscillator strength. Sunspots being cooler than the photosphere are the hosts to a large number of molecular species. However, owing to photospheric radiation scattered into the observed umbra, the discoverers could not detect the lines of SH in the sunspot spectrum where they are expected to show larger than the photospheric equivalent widths (EWs in short). Detection of weak lines in photospheric spectrum coupled with a no-detection of the relatively strong same lines in the sunspot spectrum might cause doubts on the detection itself. The above problem is investigated here in detail with a choice on photospheric and sunspot models and micro-turbulence values. The new results indicate that the predicted sunspot lines are about half intense than reported before and the lines remain of detectable strengths. Further, a need for a laboratory determination of oscillator strengths is felt.

Transition Probabilities and Oscillator Strengths for E1 Transitions of Ce III

The lanthanide elements (Z = 57−71) are important in astrophysics in relation to nucleosynthesis and star formation considerations. Spectroscopic investigations of the doubly ionized elements of this group are motivated by astrophysical interest because, in the hot chemically peculiar (CP) stars, there is an overwhelming presence of lines belonging to the third spectrum which corresponds to the dominant ionization stage [1]. The rare-earth element cerium has a particularly rich, even by rare-earth standards, optical emission spectrum from both its neutral and singly ionized stages. This characteristic has made cerium attractive for use in highintensity discharge light sources where it improves both luminous e cacy and colour rendering [2]. The works for energy levels and lifetimes of doubly ionized cerium (Ce III) can be found in, for example, [3 7]. Many strong lines of cerium in the ultraviolet evidently arise from doubly ionized atoms. King and King published a list of these [8]. Triplet and singlet terms of Ce III were reported by Russell et al. [9]. Observations of the third spectrum of cerium from 757 to 11091 A were given by Sugar [10]. The 4f 4f5d lines of Ce III were measured by Johansson and Litzen [11]. Bord and co-workers calculated oscillator strengths for some Ce III lines [12]. Later, the spectroscopic analysis of Ce III was extended. Wyart and Palmeri gave a list of computed oscillator strengths for some selected transitions [6]. Transition probabilities for Ce III were obtained from branching fractions calculated by Cowan code and experimental lifetimes by Li and co-workers [7]. Biemont et al. emphasized the importance of corepolarization e ects on oscillator strength determination in Ce III [1]. The multicon guration Dirac Fock calculation of the transition energies and oscillator strengths for the 6s S0 6s6p P1, P1 transitions in rare earth

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.

An alternative method for determination of oscillator strengths: The example of Sc II

We describe our method for determining oscillator strengths and hyperfine structure splittings that is an alternative to the commonly used, purely theoretical calculations, or to the semi-empirical approach combined with theoretically calculated transition integrals.We have developed our own computer programs that allow us to determine all attributes of the structure of complex atoms starting from the measured frequencies emitted by the atoms. As an example, we present the results of the calculation of the structure, electric dipole transitions, and hyperfine splittings of Sc II. The angular coefficients of the transition matrix in pure SL coupling were found from straightforward Racah algebra. The transition matrix was transformed into the actual intermediate coupling by the fine structure eigenvectors obtained from the semi-empirical approach. The transition integrals were treated as free parameters in the least squares fit to experimental gf values. For most transitions, the experimental and the calculated gf-values are consistent with the accuracy claimed in the NIST compilation.

Determination of oscillator strength of confined excitons in a semiconductor microcavity

We have achieved a significant experimental Rabi-splitting (3.4 meV) for confined polaritons in a planar semiconductor $\lambda$ microcavity for only a single quantum well (SQW) of GaAs (10 nm) placed at the antinode. The Rabi-splitting phenomena are discussed in detail based on the semiclassical theory, where two coupled harmonic oscillators (excitons and photons) are used to describe the system. In this way, we can obtain the dispersion curve of polaritons, the minimum value for the cavity reflectance and the oscillator strength to reach the strong coupling regime. This approach describes an ensemble of excitons confined in a SQW and includes a dissipation component. The results present a weak coupling regime, where an enhanced spontaneous emission takes place, and a strong coupling regime, where Rabi-splitting in the dispersion curve can be observed. The theoretical results are confronted with experimental data for the reflectance behavior in resonant and off-resonant conditions and present a great accuracy. This allows us to determine the oscillator strength of the confined excitons in the SQW with great precision.

Spectroscopic characterization and pulsed laser operation of Eu3+:KGd(WO4)2 crystal

Europium-doped monoclinic potassium gadolinium tungstate KGd(WO4)2 crystals are grown by the top-seeded solution growth (TSSG) technique. Their absorption spectra are studied in detail for principal light polarizations, E ∥ Np, Nm and Ng. It is accompanied by determination of absorption oscillator strengths by means of the theory of f–f transition intensities for systems with anomalously strong configuration interaction. Spectral and temporal characteristics of luminescence associated with 5D0 → 7FJ transitions are analyzed, and luminescence branching ratios and the radiative lifetime of the 5D0 state are determined. Stimulated-emission cross-section spectra are evaluated for Eu:KGd(WO4)2 crystal. Pulsed Eu:KGd(WO4)2 lasers operating at room temperature at the wavelength of 702.8 nm (5D0 → 7F4 transition) are studied at Eu concentration of 10/25 at.%. Under laser pumping at 533.6 nm, a maximum output energy of 570 μJ is obtained. The main limitation for laser operation at 5D0 → 7F2 transition is strong excited-state absorption via the 5D0 → 5F4 channel.

Determination of oscillator strength of caffeine and caffeine in tea leaves by the integrated absorption coefficient technique at two different temperatures

In this paper, oscillator strength of caffeine in dichloromethane, water, chloroform, and ethyl acetate were calculated in the wave number range of 32, 000 to 41,000cm-1. It was found that oscillator strength of caffeine in dichloromethane, water, chloroform, and ethyl acetate were 0.230 ± 0.001, 0.170 ± 0.0003, 0.114 ± 0.001, 0.150 ± 0.001 respectively. Caffeine content of real tea leaves using integrated absorption coefficient method were also calculated for different samples at two different temperatures. The result agrees with that obtained using Beer’s law with a little less in the case of integrated absorption coefficient technique with higher value at the boiling temperature and smaller extraction time. Key words: Tea leaves, integrated absorption coefficient, caffeine, oscillator strength, UV-visible spectroscopy.

“Solar” oscillator strength scale and determination of the LTE silicon abundance in the solar atmosphere

We determine LTE abundance of silicon from 65 lines of Si I using one-dimensional semiempirical models of the solar atmosphere HOLMUL, MACKKL, and VAL,C. Our list of lines is considerably larger than lists used earlier. We confirm the reliability of the oscillator strength scale of E.A. Gurtovenko and R.I. Kostik for Si I lines that was based on the fitting to the observed solar equivalent widths. It is shown that this scale is displaced by +0.073 dex and −0.026 dex from experimental scales derived by Becker et al. and Garz, respectively. The difference between “solar” and experimental oscillator strength scales hardly depends on their lower excitation potentials, wavelengths, and equivalent widths. This difference can be interpreted as a total error caused by the choice of the one-dimensional model of atmosphere, the neglect of NLTE effects, the ignoring of the granulation, errors of the van der Waals damping constant, the microturbulence velocity, and the observed equivalent width. We study the effect of changes in various input parameters on the obtained LTE abundance of silicon and show that both the experimental scale of Becker et al. and the displaced “solar” scale produce almost the same silicon abundance. A total root-mean-square error of the abundance, which is caused by errors in equivalent widths and the microturbulence velocity, is 0.02 dex. The use of the semiclassical theory of Anstee, Barklem, and O’Mara for the description of the van der Waals damping constant leads to the emergence of a correlation of the abundance obtained from Si I lines with the equivalent width. There is no such correlation when using the classical Unsold approximation with an enhancement factor E = 1.5. On average, differences in abundances obtained using the mentioned approximations do not exceed 0.03 dex. At E = 1.5, the LTE silicon abundance calculated using the HOLMUL model with “solar” oscillator strengths referred to the experimental scale of Becker et al. is equal to 7.594 ± 0.015, whereas the LTE silicon abundance calculated using the VAL,C model is 7.623 ± 0.021.

Evidence of excitonic transitions by angle‐resolved reflectivity for the determination of oscillator strengths in GaN/(Al,Ga)N quantum wells

AbstractWe report on a study of the excitonic properties of GaN/AlxGa1‐xN quantum well samples using continuous‐wave reflectivity and photoluminescence measurements. Weak excitonic signals superposed to large oscillations resulting from the interferences in the buffer layers are highlighted by angle‐resolved reflectivity. The quantum well excitonic oscillator strength was determined from the fitting of the experimental spectra and the influence of aluminum concentration of the barrier was also investigated (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Theoretical determination of oscillator strengths for the principal series of rubidium-like ions by the Dirac-Fock method

A simple formula that allows the determination of the oscillator strengths for all transitions of principal series of the Rb-like ions is obtained from the relationship between the oscillator strengths and the corresponding photoionization cross sections. The photoionization cross sections are calculated by the Dirac-Fock method with allowance for the retardation and approximated by an analytic formula. The data for ten ions of the rubidium isoelectronic sequence (from Sr+ to Ag10+) are presented. Two types of gauges corresponding to the transition operators in length and velocity forms are considered.

In search of the s-process in cool supergiants: a vital role for laboratory astrophysics

We report on progress in determining the chemical composition of the photospheres of massive, cool supergiant stars for the purpose of investigating whether by-products from recent slow neutron capture nucleosynthesis have been transported up to the photosphere by convective processes. Our initial work has been focused on identifying atomic transitions that are useful for stellar abundance work at near-infrared wavelengths and in gathering accurate atomic data for these transitions. The latter task includes the determination of experimental oscillator strengths, which represents a vital role for laboratory astrophysics. We use high-resolution optical and near-infrared spectra of the massive, cool star α. Orionis as the prototype for our study for line identification and synthetic spectrum modeling. Abundances have been determined for a number of heavy elements, and our early results illuminate the problems with atomic data that must be overcome before we are able to derive chemical abundances with the accuracy required for meaningful comparison with calculations for s-process nucleosynthesis.

Oscillator strengths for ultraviolet transitions in P II and Cu II

Analysis of ultraviolet absorption from the dominant ions in interstellar clouds provides information on the mineralogy of the solid material in space and on the synthesis of elements in our Galaxy and beyond. For the most part the spectra are acquired with the spectrometers on the Hubble Space Telescope and the Far Ultraviolet Spectroscopic Explorer. In order to convert the amount of absorption into an accurate abundance, determinations of oscillator strengths of sufficiently high quality are needed. We present our most recent beam-foil measurements in this area. Lifetimes, branching fractions, and oscillator strengths for all transitions within the P II multiplet at 1154 Å are compared with available results. Close agreement between our laboratory measurements and theoretical and semi-empirical calculations suggests a means for calibrating fast-beam instruments in the far ultraviolet. As for Cu II, our results for the line at 1358 Å provide further evidence for a short lifetime for the upper state of interest.

Excitation of the A 2Σ +, C 2Π and D 2Σ + Rydberg-electronic states in NO by 100 eV electrons

We report differential cross sections and optical oscillator strength determinations for the respective excitation of vibrational sub-levels of the A 2Σ +, C 2Π and D 2Σ + electronic states in NO by 100 eV electrons. While the differential cross section measurements are original, the present optical oscillator strengths are compared where possible with earlier values. In particular, a detailed comparison is made with the dipole (e,e) spectroscopy data from Chan et al. [W.F. Chan, G. Cooper, C.E. Brion, Chem. Phys. 170 (1993) 111], with generally very good agreement being found.

Continuous wave and ultra-fast reflectivity studies for the determination of GaN excitonic oscillator strengths as a function of the in-plane biaxial strain

Abstract Up to now, many works have been dedicated to the study of the excitonic parameters of GaN by analyzing cw-spectroscopy results. In this work, time-resolved reflectivity experiments are carried out to record the impulse response of excitons at the femtosecond scale. By combining the analysis of continuous wave and time-resolved reflectivity spectra recorded on high quality GaN samples, the excitonic parameters are determined with accuracy. The oscillator strength evolutions of A, B and C free excitons are analysed versus the in-plane biaxial stress and compared with theoretical predictions.