New accurate data for the spectrum of neutral silver

Pickering, J. C.; Zilio, Valéry Olivier

doi:10.1007/s100530170264

Cited by 71 publications

(31 citation statements)

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“…The absolute wavelengths of the different components were derived from the centre of gravity of the resonance lines measured by Pickering & Zilio (2001), who used a hollow cathode discharge and Fourier Transform Spectrometer. The hyperfine and isotopic structure are too small to be resolved in the Doppler broadened line profiles.…”

Section: Hyperfine Structure Componentsmentioning

confidence: 99%

Silver and palladium help unveil the nature of a second r-process

Hansen

Primas

Hartman

et al. 2012

A&A

145

204

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Context. The rapid neutron-capture process, which created about half of the heaviest elements in the solar system, is believed to have been unique. Many recent studies have shown that this uniqueness is not true for the formation of lighter elements, in particular those in the atomic number range 38 < Z < 48. Among these, palladium (Pd) and especially silver (Ag) are expected to be key indicators of a possible second r-process, but until recently they have been studied only in a few stars. We therefore target Pd and Ag in a large sample of stars and compare these abundances to those of Sr, Y, Zr, Ba, and Eu produced by the slow (s-) and rapid (r-) neutron-capture processes. Hereby we investigate the nature of the formation process of Ag and Pd. Aims. We study the abundances of seven elements (Sr, Y, Zr, Pd, Ag, Ba, and Eu) to gain insight into the formation process of the elements and explore in depth the nature of the second r-process. Methods. By adopting a homogeneous one-dimensional local thermodynamic equilibrium (1D LTE) analysis of 71 stars, we derive stellar abundances using the spectral synthesis code MOOG, and the MARCS model atmospheres. We calculate abundance ratio trends and compare the derived abundances to site-dependent yield predictions (low-mass O-Ne-Mg core-collapse supernovae and parametrised high-entropy winds), to extract characteristics of the second r-process. Results. The seven elements are tracers of different (neutron-capture) processes, which in turn allows us to constrain the formation process(es) of Pd and Ag. The abundance ratios of the heavy elements are found to be correlated and anti-correlated. These trends lead to clear indications that a second/weak r-process, is responsible for the formation of Pd and Ag. On the basis of the comparison to the model predictions, we find that the conditions under which this process takes place differ from those for the main r-process in needing lower neutron number densities, lower neutron-to-seed ratios, and lower entropies, and/or higher electron abundances. Conclusions. Our analysis confirms that Pd and Ag form via a rapid neutron-capture process that differs from the main r-process, the main and weak s-processes, and charged particle freeze-outs. We find that this process is efficiently working down to the lowest metallicity sampled by our analysis ([Fe/H] = −3.3). Our results may indicate that a combination of these explosive sites is needed to explain the variety in the observationally derived abundance patterns.

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Section: Hyperfine Structure Componentsmentioning

confidence: 99%

Silver and palladium help unveil the nature of a second r-process

Hansen

Primas

Hartman

et al. 2012

A&A

145

204

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“…In this respect, the energy level structure of Ag nanoclusters turns out to be more difficult to model. This is simply due to already complex structure of the energy states of even a single Ag atom now multiplied by a strong coupling between spin and orbit motions of delocalized Ag electrons, 9 plus a mixing the energy states of the Ag atoms in the nanoclusters 1-8 and in addition an effect of the ligands. 10 As far as we are aware, relatively little is known from the literature about interpretation and modeling of the optical spectra of Ag nanoclusters consisting of only few Ag atoms, 1-10 especially when the nanoclusters are embedded in a solid host.…”

Section: Introductionmentioning

confidence: 99%

Experiment and theoretical modeling of the luminescence of silver nanoclusters dispersed in oxyfluoride glass

Cuong

Tikhomirov

Chibotaru

et al. 2012

The Journal of Chemical Physics

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Density functional theory (DFT) and complete active space perturbation theory (CASPT2) have been applied for modeling the configuration, charge, energy states, and spin of luminescent Ag nanoclusters dispersed within the bulk of oxyfluoride glass host. The excitation spectra of luminescence of the Ag nanoclusters have been measured and simulated by means of the DFT and CASPT2. Electron spin resonance spectra have been recorded and suggest diamagnetic state of Ag nanoclusters. The silver nanoclusters have been argued to consist mostly of pairs of Ag(2) (+) dimers, or Ag(4) (2+) tetramers, with different extent of distortion along the tetramer diagonal. The sites for the Ag nanoclusters have been suggested where the pairs of Ag ions substitute onto metal and hole cation sites and are surrounded by fluorine ions within a fluorite-type lattice.

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“…Table 7 presents the energies of the Ag levels involved in the observed transitions. Their uncertainties are lower than those for Au and Cu (see Table 9 below), since for the Ag levels we used the high-accuracy reference values published by Pickering and Zilio (2001). Most of the values do not differ much from the previous measurement and from other sources.…”

Section: Agmentioning

confidence: 99%