UV Transitions Research Articles

Metal-poor star formation at z > 6 with JWST: new insight into hard radiation fields and nitrogen enrichment on 20 pc scales

ABSTRACT Nearly a decade ago, we began to see indications that reionization-era galaxies power hard radiation fields rarely seen at lower redshift. Most striking were detections of nebular C iv emission in what appeared to be typical low-mass galaxies, requiring an ample supply of 48 eV photons to triply ionize carbon. We have obtained deep JWST/NIRSpec R = 1000 spectroscopy of the two z > 6 C iv-emitting galaxies known prior to JWST. Here, we present a rest-UV to optical spectrum of one of these two systems, the multiply-imaged z = 6.1 lensed galaxy RXCJ2248-ID. NIRCam imaging reveals two compact (<22 pc) clumps separated by 220 pc, with one comprising a dense concentration of massive stars (>10 400 M⊙ yr−1 kpc−2) formed in a recent burst. We stack spectra of 3 images of the galaxy (J = 24.8–25.9), yielding a very deep spectrum providing a high-S/N template of strong emission line sources at z > 6. The spectrum reveals narrow high-ionization lines (He ii, C iv, N iv]) with line ratios consistent with powering by massive stars. The rest-optical spectrum is dominated by very strong emission lines ([O iii] EW = 2800 Å), albeit with weak emission from low-ionization transitions ([O iii]/[O ii] = 184). The electron density is found to be very high (6.4–31.0 × 104 cm−3) based on three UV transitions. The ionized gas is metal poor ($12+\log (\rm O/H)=7.43^{+0.17}_{-0.09}$), yet highly enriched in nitrogen ($\log (\rm N/O)=-0.39^{+0.11}_{-0.10}$). The spectrum appears broadly similar to that of GNz11 at z = 10.6, without showing the same AGN signatures. We suggest that the hard radiation field and rapid nitrogen enrichment may be a short-lived phase that many z > 6 galaxies go through as they undergo strong bursts of star formation. We comment on the potential link of such spectra to globular cluster formation.

Effect of Blending Cotton/Bamboo on UV Protection and Functional Purposes of Trilobal Polyester Microfibers Knitted Fabrics Using Different Structures

Resistance to ultraviolet radiation and electrostatic charge is a basic property that must be considered in the manufacture of fabrics, particularly in light of the climate changes affecting people around the world in various regions, especially in subtropical and tropical regions. It has thus become necessary to focus on the use of different natural fibres to mitigate UV transitions and the formation of electrostatic charges. The aim of this research was to enhance the protection of the ultraviolet effect and reduce electrostatic charge formation by blending cellulose yarns (bamboo and cotton) with trilobal polyester microfiber yarn that has characteristics such as lightweight, low-thickness, high strength, and shine. Knitted samples were produced from two different structures according to their tightness factor (single jersey and fleece structures), the various functional properties of the produced fabrics, such as mass per unit area, thickness, air and water permeability, and bursting strength, were tested. The properties of electrostatic charge and the ultraviolet protection factor (UPF) were also determined. The findings indicate that the samples produced with bamboo resulted in a preferable performance with different structures, especially when considering electrostatic charge and UPF properties. Moreover, the fleece structure had a more significant effect on knitted samples’ behaviour than the single jersey (plain) structure.

Phosphorescence by Trapping Defects in Boric Acid Induced by Thermal Processing

AbstractThe phosphorescence of boric acid (BA, H3BO3) at room temperature is a puzzling phenomenon subject to controversial interpretations although the role of structural defects has not yet been considered. Heat treatments of boric acid cause its transformation into the metaboric phase and amorphous boron oxide (B2O3). The structural changes after thermal processing can create defects that become centers of luminescence and recombination channels in the visible range. In the present work, commercial boric acid is thermally processed at different temperatures. Samples treated between 200 and 400 °C exhibit remarkable phosphorescence in the visible range. At ≈480 and 528 nm, two distinct phosphorescent emissions occur, associated with trapped charge carriers recombinations identified by thermoluminescence (TL) and electron paramagnetic resonance spectroscopy (EPR). The structural and optical studies suggest that the activation of boric acid phosphorescence after heat treatment is correlated with the presence of defects. The afterglow results from a trapping and detrapping process, which delays the recombination at the active optical centers. Time‐dependent density functional study (DFT) of defective BOH molecules and clusters shows the emergence of near UV and blue optical transitions in absorption. These defects trigger the photoluminescence in thermally processed boric acid samples.

Branching Fractions and Transition Probabilities for UV Transitions in the Spectrum of Cr ii

We present transition probabilities for 268 spectral lines of singly ionized chromium (Cr ii) in the wavelength region 208–414 nm. Branching fractions were measured in archival Fourier transform spectra of chromium-argon and chromium-neon hollow cathode lamps and a Penning discharge source. The branching fractions were combined with previously published experimental lifetimes of 14 levels, and with lifetimes from semiempirical calculations for 14 levels to give transition probabilities. The estimated uncertainties of the transition probabilities range from 10% to 26%. A comparison with previously published experimental transition probabilities shows discrepancies of up to a factor of 2.5 for lines around 213 nm.

Synchrotron-based UV resonance Raman spectroscopy probes size confinement, termination effects, and anharmonicity of carbon atomic wires

Vibrational and electronic properties and anharmonicity of sp-carbon atomic wires (i.e., polyynes) have been studied using resonance Raman spectroscopy, focusing on the confinement effects connected to their structure (length and termination). We exploited the fine tunability of the synchrotron radiation to resonantly excite short H-, CH3-, and CN-capped carbon atomic wires at their vibronic transitions in the deep UV. We report for the first time the resonance Raman spectra of size-selected CH3-capped polyynic wires (HCnCH3, n = 8–12) and CN-capped wires (HC6CN and HC12CN). We observed that the degree of π-electron conjugation increases with the wire length and is related to the specific termination. The analysis of multiple quanta Raman overtone bands shows that the anharmonic correction of the vibrational potential energy becomes increasingly relevant as the wire length increases. Finally, studying the vibronic lines of the UV absorption spectra allows the determination of an effective displacement parameter between the minima of the ground and the low-lying excited state, proving that the strong electron-phonon coupling of these systems is sensitive to chain length and termination.

Synthesis, characterization and biological evaluation of piperazine embedded copper complexes

In this paper, we report the synthesis, and characterization of three piperazine based multidentate ligands and their copper complexes. Ligands and complexes were characterized by UV–Vis, FT–IR, 1H NMR and mass spectra along with EPR spectra, molar conductance and thermogravimetric analysis (TGA). The metal complexes showed peaks corresponding to ligand to Cu(II) LMCT transition in UV–Vis spectrum. Molar conductance values of all complexes studied in water and DMSO indicated nonionic nature of complexes. TGA derivative curve represented the initial loss of water, which was in agreement of coordinated water in the proposed complexes. Four coordinated copper complexes were proposed on the basis of spectral data and supported by mass fragmentation pattern, isotopic distribution pattern, EPR, molar conductance and TGA. Ligands and complex geometries were optimized using DFT calculations and TDDFT studies of ligands were performed to corroborate the experimental UV–Vis spectrum. These ligands and complexes were tested for antibacterial activity and all complexes showed higher activity as compared to ligands. Antioxidant behavior of complexes was investigated by DPPH (2,2-diphenyl-1-picrylhydrazyl) method, and percentage inhibition data suggested two complexes Cu2L1 and Cu2L3 to hold fair antioxidant potential. In vitro cytotoxic studies of complexes performed on breast cancer cell line (MCF–7) using MTT calorimetric assay and IC50 value indicated good cytotoxic potential. BSA binding studies and DNA binding studies with CT-DNA were performed using UV–Vis titrimetric methods and were supported by molecular docking studies of complexes to investigate available binding interactions sites.

Theoretical Characterization of Carbonic Acid Clusters in the UV.

Two theoretical structural motifs are proposed to match two experimental solid carbonic acid UV spectra from previous literature ( Astron. Astrophys. 2021, 646, A172): a linear ribbon structure as a single octamer and nonplanar orientations of carbonic acid clusters. The latter have some contribution from approximated amorphous solid carbonic acid in the form of 40 different clusters of 8 carbonic acid molecules ensemble-averaged together, but unoptimized pairs of optimized dimers oriented perpendicular to one another give the strongest intensities of lower energy UV transitions. The linear ribbon structure's predicted spectrum computed with CAM-B3LYP/6-311G(d,p) agrees well with Experimental Solid B─the β-carbonic acid experimental data in the UV region. Meanwhile, the 40 amorphous clusters are built with a randomization script, and the electronically excited states are calculated with both CAM-B3LYP/6-311G(d,p) and ωB97XD/6-311G(d,p). The resulting theoretical spectrum is constructed by employing a Boltzmann distribution of the intensities and artificially broadening the simulated spectra. The nonplanar dimer pairs are computed with CAM-B3LYP and B3LYP with the 6-311G(d,p) basis set. The results of the amorphous simulation weakly correspond with the Experimental Solid A spectrum, but the fully nonplanar motif matches the experiment much more convincingly. As a result, the previous work appears to have observed the traditional crystalline phase of solid carbonic acid in Experimental Solid B, whereas the nonplanar orientations of the carbonic acids in the clusters appear to correlate with Experimental Solid A. This spectral classification will aid in future laboratory work exploring the role that carbonic acid can play in low temperature, low pressure desorbed environments with potential application to astrochemistry.

Femtosecond ultraviolet laser absorption spectroscopy for simultaneous measurements of temperature and OH concentration

This Letter reports a femtosecond ultraviolet laser absorption spectroscopy (fs-UV-LAS) for simultaneous in situ measurements of temperature and species. This fs-UV-LAS technique was demonstrated based on X2Π-A2Σ+ transitions of OH radicals near 308 nm generated in low temperature plasmas and flames. The fs-UV-LAS technique has revealed three major diagnostic benefits. First, a series of absorption features within a spectral bandwidth of ∼3.2 nm near 308 nm were simultaneously measured and then enabled simultaneous multi-parameter measurements with enhanced accuracy. The results show that the temperature and OH concentration could be measured with accuracy enhanced by 29–88% and 58–91%, respectively, compared to those obtained with past two-narrow-line absorption methods. Second, an ultrafast time resolution of ∼120 picoseconds was accomplished for the measurements. Third, due to the large OH X2Π-A2Σ+ transitions in the UV range, a simple single-pass absorption with a 3-cm path length was allowed for measurements in plasmas with low OH number density down to ∼2 × 1013 cm−3. Also due to the large OH UV transitions, single-shot fs absorption measurements were accomplished in flames, which was expected to offer more insights into chemically reactive flow dynamics.

Synthesis, crystal structure, spectroscopic, quantum chemical investigation, molecular docking and ADMET prediction of 2(E)-3-(anthracen-9-yl)-1-(1-methyl-1H-pyrrol-2-yl) prop-2-en-1-one

In the present study, 2(E)-3-(anthracen-9-yl)-1-(1-methyl-1H-pyrrol-2-yl) prop-2-en-1-one (3AMP) crystal was grown by slow evaporation method. The single crystal X-ray diffraction analysis and density functional theory (DFT) calculations were carried out for 3AMP crystal. The 3AMP crystallizes in orthorhombic space group Pbca with a = 14.818 (8) Å, b = 9.796 (5) Å, c = 23.239 (11) Å. Hirshfeld surface and finger print plots were analyzed to confirm the existence of intra-, inter-molecular and other weak interactions using Crystal Explorer. The optimized molecular structure and harmonic wavenumbers were calculated by DFT method using B3LYP functional with 6-31G(d,p) basis set. The FT-IR, 1H, 13C NMR and UV–Vis spectra of 3AMP were recorded and analyzed. The optimized geometrical parameters, calculated wavenumbers by DFT method were compared with the experimental results. Natural bond orbital (NBO) analysis was carried out to evaluate the intra- and inter-molecular interactions in the crystal. The energy gap for 3AMP was calculated as 3.156 eV. Molecular electrostatic potential (MEP), Mulliken atomic charges and non-linear optical (NLO) properties for the title crystal were calculated. In addition, gauge invariant atomic orbital (GIAO) method was used to calculate the 1H and 13C NMR chemical shifts in the ground state. To obtain the electronic transitions in UV–Vis spectra of the title molecule in DMSO and ethanol solvents, TD-DFT calculations were performed on the optimized geometry. Furthermore, the compound was subjected to in silico ADMET evaluation. Molecular docking study was carried out to determine the interactions of ligand with the protein Hyaluronidase (PDB ID: 1FCQ).

Synthesis and characterization of novel hybrid compounds containing coumarin and benzodiazepine rings based on dye

AbstractCoumarin derivatives, one of the organic fluorescent materials, are widely applied in many areas such as laser dyes, organic light emitting diodes (OLED), pharmaceuticals and bio/chemosensors, with the advantages of the large conjugated system and planar structure. In the coumarin analogs, which are polarity sensitive fluorophores, a shift to the red zone is observed in the case of π expansion at 3‐positions and electron donor groups at 7‐positions. The present article reports the synthesis of novel hybrid compounds (CD1‐CD8) containing coumarin and benzodiazepine rings using ethyl 3‐(7‐(diethylamino)‐2‐oxo‐2H‐chromen‐3‐yl)‐3‐oxopropanoate reagent and 1,2‐diaminobenzene derivatives under optimized reaction conditions with PTSA catalyst. The structures of target compounds synthesized were characterized by FTIR, 1HNMR, 13CNMR, HRMS and UV–Vis spectra. The effects of electron withdrawing and electron donor groups in the cyclocondensation reaction that takes place as regioselective were evaluated in detail. The substituent effects were investigated for n‐π* and π‐π* electronic transitions in UV–Vis Spectroscopy.

Improved Atomic Transition Probabilities for UV and Optical Lines of Hf II and Determination of the Hf Abundance in Two Metal-poor Stars*

Abstract We report new branching fraction measurements for 199 UV and optical transitions of Hf ii. These transitions range in wavelength (wavenumber) from 2068 to 6584 Å (48,322–15,183 cm−1) and originate in 17 odd-parity upper levels ranging in energy from 38,578 to 53,227 cm−1. The branching fractions are combined with radiative lifetimes reported in an earlier study to produce a set of transition probabilities and log(gf) values with accuracy ranging from 5% to 25%. Comparison is made to transition probabilities from the literature where such data exist. We use these new transition probabilities to derive improved Hf abundances in two metal-poor stars. HD 196944 is enhanced in s-process elements, and we derive log ε (Hf) = −0.72 ± 0.03 (σ = 0.09) from 12 Hf ii lines. HD 222925 is enhanced in r-process elements, and we derive log ε (Hf) = 0.32 ± 0.03 (σ = 0.11) from 20 Hf ii lines. These measurements greatly expand the number of potentially useful Hf ii lines for analysis in UV and optical spectra.

Reevaluation of Cr6+ optical transitions through Gd2O3 doping of chromium-borate glasses

Abstract Chromium-doped borate glasses are appealing for potential optical applications as they feature distinct optical transitions in the visible and ultraviolet spectral regimes. However, such intense UV transitions are often screened in borate glasses due to their proximity to the bulk absorption edge. Here, we utilize variable concentrations of the wide band gap Gd2O3 dopant to detach these near-edge optical transitions. The amorphous nature of all Gd2O3-doped borate glass samples, containing a fixed Cr amount, was confirmed by X-ray diffraction. Gd2O3 additives were found to enforce the compactness of the glassy network as inferred from the increased experimental density and calculated average boron-boron separation. Analysis of the infrared spectra revealed the essential vibration modes of structural units, the non-bridge oxygen, and the fraction of tetrahedrally-coordinated boron atoms ratios. These ratios together with a noticeable BO3 to BO4 conversion suggest an open glass structure with enlarged band gap energy. The latter is confirmed by recording the optical absorption spectra for all samples, which exhibited clear blue shifts of the absorption edge and an estimated wide band gap of size ~3.38 eV. In addition to Cr3+ transitions manifesting in the visible region, two well-resolved ultra-violet transitions characteristic for Cr6+ were unambiguously identified down to ~339 nm. These transitions and other relevant quantities, such as crystal field strength and Racah parameters, were accurately determined from a deconvolution process applied to all optical spectra. The present Gd2O3-doped glasses offer wide band gap materials with high energy optical transitions suitable for UV optics, such as ultraviolet digital photography and insect light traps.

Excitation energies, transition data of SXR, HXR, EUV and far-UV spectral lines with partition function, thermodynamic parameters and level population for W LXVII and W XLIX

We present excitation energies, emitted photon wavelength during the transition from upper level to lower level, lifetimes, transitions rates and other transition parameters for first fine structure 200 levels of W LXVII and W XLIX by using Multi-Configuration Dirac-Fock (MCDF) scheme in our calculations. We endorse that contributions of relativistic effects QED and Breit corrections in energies of levels are significant. We have also shown that our results of energies from both, Flexible Atomic Code (FAC) and General Purpose Atomic Structure Package (GRASP) matches with each other and also with NIST and other experimentally measured and theoretically calculated results. We have predicted all soft x-ray (SXR), hard x-ray (HXR), extreme ultraviolet (EUV) and far UV transitions from ground state in W LXVII and W XLIX. Furthermore, we have also provided relative population for first five excited states, partition function and thermodynamic quantities for both W LXVII and W XLIX and studied their variations with temperature. Besides, detailed new atomic data and thermodynamic data of W LXVII and W XLIX which are not published so far in the literature have been reported and can be advantageous in the field of modelling of fusion and astrophysical plasmas, cell biology and microscopic imaging.

Physical conditions of five O vi absorption systems towards PG 1522+101

ABSTRACT We present the analysis of five O vi absorbers identified across a redshift path of z ∼ (0.6−1.3) towards the background quasar PG 1522+101 with information on five consecutive ionization stages of oxygen from O ii to O vi. The combined HST and Keck spectra cover UV, redshifted extreme-UV, and optical transitions from a multitude of ions spanning ionization energies in the range of ∼(13−300) eV. Low-ionization (C ii, O ii, Si ii, Mg ii) and very high-ionization species (Ne viii, Mg x) are non-detections in all the absorbers. Three of the absorbers have coverage of He i, in one of which it is a >3σ detection. The kinematic structures of these absorbers are extracted from C iv detected in HIRES spectra. The farthest absorber in our sample also contains the detections of Ne v and Ne vi. Assuming co-spatial absorbing components, the ionization models show the medium to be multiphased with small-scale density–temperature inhomogeneities that are sometimes kinematically unresolved. In two of the absorbers, there is an explicit indication of the presence of a warm gas phase (T ≳ 105 K) traced by O vi. In the remaining absorbers, the column densities of the ions are consistent with a non-uniform photoionized medium. The subsolar [C/O] relative abundances inferred for the absorbers point at enrichment from massive Type II supernovae. Despite metal enrichment, the inferred wide range for [O/H] ∼ [−2.1, +0.2] amongst the absorbers along with their anticorrelation with the observed H i suggest poor small-scale mixing of metals with hydrogen in the regions surrounding galaxies and the IGM.

Purification and characterization of two killer toxins originated from Torulaspora delbrueckii (Lindner) and Wickerhamomyces anomalus (E.C.Hansen) Kurtzman, Robnett, and Basehoar-Powers

BackgroundEcological killer yeasts have had few studies compared with laboratory killer yeasts. The killer yeasts are known in excreting killer toxins that kill sensitive or susceptible yeasts. The killer toxins, such as TK and WK excreted from two yeast isolates (Torulaspora delbrueckii and Wickerhamomyces anomalus) have protenious nature with different molecular weight depending on yeast species.ResultsA qualitative test was conducted to determine the ability of both isolates to produce killer toxins on the media of yeast extract and malt extract broth when the two toxins were first purified by ammonium sulfate salt at 40% concentration and then by dialysis for the killer toxin TK and gel filtration method for WK. The molecular weight of TK was estimated at about 15 kDa, while WK was at 45 kDa. The chemical properties of the killer toxins were also studied. The results showed that the two killer toxins were with protenious nature.ConclusionBoth yeast isolates (Torulaspora delbrueckii and Wickerhamomyces anomalus) had the ability of producing different kinds of killer toxins. The two killer toxins (TK and WK) were identified for the first time in Iraq, and their production involves many steps of economically unexpansive purification method with a good quality and high purity of producing killer toxins. The results confirmed that the nature of killer toxins (WK and TK) was similar to protein compounds resulted from the transition in UV and functional groups.

Vibration mediated photodissociation dynamics of CH3SH: manipulation of the dynamic energy disposal into products.

The S-H bond dissociation dynamics of CH3SH have been investigated for the S1-S0 transition mediated by either the S-H stretching (2608 cm-1) or CH3 symmetric stretching (2951 cm-1) mode excitation in the S0 state. The S-H and C-S bond extensions are strongly coupled in the S1 state through the S1/S2 same-symmetry conical intersection, giving the C-S stretching mode excitation of the CH3S˙ fragment during the prompt S-H bond rupture on S1. In the IR + UV transition mediated by the S-H stretching mode, the vertical transition seems to access the Franck-Condon region where the S-H bond is shortened while the coupling to the C-S bond stretching becomes stronger compared to the case of one-photon UV transition, indicating that the intramolecular vibrational redistribution (IVR) is little activated in S0. When the IR + UV excitation is mediated by the CH3 symmetric stretching mode, on the other hand, the Franck-Condon region in S1 encompasses the enlarged molecular structures with respect to both S-H and C-S bond extensions, presumably due to the rapid IVR in S0 prior to the vertical transition. This leads to the inverted vibrational state population of the C-S bond stretching mode of the CH3S˙ fragment. This work demonstrates that the reaction dynamics upon the IR + UV excitation of CH3SH is highly mode dependent and the energy disposal dynamics could be controlled by the manipulation of the Franck-Condon region through the particular vibrational-state mediation in the ground state, shedding new light on the structure-dynamics relationship.

The NLTE Analyses of Carbon Emission Lines in the Atmospheres of O- and B-type Stars

We present a model atom for C I - C II - C III - C IV using the most up-to-date atomic data and evaluated the non-local thermodynamic equilibrium (NLTE) line formation in classical 1D atmospheric models of O-B-type stars. Our models predict the emission lines of C II 9903~\AA\ and 18535~\AA\ to appear at effective temperature \Teff~$\geq$~17\,500~K, those of C II 6151~\AA\ and 6461~\AA\ to appear at \Teff~$>$~25\,000~K, and those of C III 5695, 6728--44, 9701--17~\AA\ to appear at \Teff~$\geq$~35\,000~K (log~$g$=4.0). Emission occurs in the lines of minority species, where the photoionization-recombination mechanism provides a depopulation of the lower levels to a greater extent than the upper levels. For C II 9903 and 18535~\AA, the upper levels are mainly populated from C III reservoir through the Rydberg states. For C III 5695 and 6728--44~\AA, the lower levels are depopulated due to photon losses in UV transitions at 885, 1308, and 1426--28~\AA\ which become optically thin in the photosphere. We analysed the lines of C I, C II, C III, and C IV for twenty-two O-B-type stars with temperature range between 15\,800 $\leq$~\Teff~$\leq$ 38\,000~K. Abundances from emission lines of C I, C II and C III are in agreement with those from absorption ones for most of the stars. We obtained log~$\epsilon_{\rm C}$=8.36$\pm$0.08 from twenty B-type stars, that is in line with the present-day Cosmic Abundance Standard. The obtained carbon abundances in 15~Mon and HD~42088 from emission and absorption lines are 8.27$\pm$0.11 and 8.31$\pm$0.11, respectively.

Two-Photon Excitation of Neat Aerated Solvents with Visible Light Produces Singlet Oxygen.

Aeration of common liquid solvents (e.g., cyclohexane, benzene, or water) gives rise to a unique absorption band associated with a transition from a ground state oxygen-solvent collision complex to an oxygen-solvent charge-transfer (CT) state. Although the absorption band is solvent-dependent, the energies involved invariably correspond to a one-photon transition in UV. We now show that this CT state can also be produced in a nonlinear two-photon process using visible light. Moreover, the CT state decays to produce an appreciable amount of singlet oxygen, O2(a1Δg). As such, we demonstrate a convenient method to generate O2(a1Δg) and oxygen-based radicals with high spatial resolution and localization control under conditions in which a photosensitizer is not added as a solute. We also provide a reasonable explanation for the undesired photoinduced oxidative degradation often observed in Raman and nonlinear optical microscopy experiments and in other laser-based applications where the solute itself does not absorb light. Finally, we provide evidence for a comparatively long-lived photoproduced species in liquid water, possibly the triplet state of water itself, that sensitizes O2(a1Δg) production.

Pyridazine N-Oxides as Precursors to 2-Aminofurans: Scope and Limitations in Complexity Building Cascade Reactions.

A method to transform pyridazine N-oxides into 2-aminofurans using a combination of UV light and transition metal catalysis has been developed. These electron-rich species exhibit a surprising range of useful reactivity, including the ability to participate in complexity building cascade processes when reacted with dienophiles. This study also establishes 2-aminofurans as valuable synthons that support modular synthetic entry to the shared heterocyclic core of certain aspidosperma and amaryllidaceae alkaloids.

Improved Ni II oscillator strengths from quasar absorption systems

Aims. We wish to improve the accuracy of oscillator strength values for several Ni II UV transitions and measure for the first time the f-value of a few other weak transitions for which no laboratory nor astronomical measurement is presently available. Methods. Four quasars displaying five damped Lyman α systems with relatively strong Ni II lines were selected. From the analysis of the excellent high resolution spectra available, we determined the relative f-value of Ni II transitions by comparing the strength of the corresponding absorption profiles. To quantify the latter, we used the apparent optical depth method for resolved features, equivalent width measurements for optically thin lines and line fitting with VPFIT. Absolute f-values were then derived by relating our determinations to the available laboratory measurements. Results. Thanks to the good signal-to-noise ratio of the spectra and to the suitable properties of the absorption systems investigated, we are able to significantly improve the determination of the f-value for 13 Ni II transitions falling in the 1317–1804 Å interval. Our results are found to be consistent with other earlier determinations for ten of these transitions; our median relative accuracy for these f-values is 6.5%. For three weak transitions near 1502, 1773, and 1804 Å, which have not been detected previously in astronomical spectra, we can get a first measurement of their f-value. Conclusions. Our work illustrates that, thanks to the redshift and the absence of variations of physical constants on cosmological scales, the analysis of absorption lines induced by remote gas in quasar spectra can nowadays provide valuable constraints on atomic data in the UV range.