Scientists map silver's atomic fingerprint to solve cosmic chemistry puzzle
Researchers have calculated precise atomic data for silver that will improve how astronomers measure the element in distant stars—refining our understanding of how heavy elements form in the universe. The work matters for validating models of stellar nucleosynthesis and could influence how space agencies prioritize observations of neutron star collisions.
Originaltitel: Accurate transition and hyperfine data in Ag I from the multiconfiguration Dirac-Hartree-Fock and relativistic coupled-cluster methods
<p><em>Context</em>. Silver is a key tracer of the weak r-process in late-type stars. However, when the assumption of local thermodynamic equilibrium is relaxed, accurate abundance determinations become even more sensitive to complete sets of reliable transition data.</p><p><em>Aims</em>. The aim of this work is to provide accurate and extensive results of excitation energies, radiative transitions, and hyperfine data for Ag I.</p><p><em>Methods</em>. The multiconfiguration Dirac-Hartree-Fock (MCDHF) and relativistic coupled-cluster (RCC) methods were used in the present work. The quantitative and qualitative evaluation approach was applied to the MCDHF transition rates to estimate uncertainties using the terminology of the National Institute of Science and Technology Atomic Spectroscopic Database (NIST ASD).</p><p><em>Results</em>. Excitation energies, transition data, and hyperfine structure constants were calculated for 18 states up to 4d<sup>10</sup>8s. Fifty-seven electric dipole (E1) transition rates and weighted oscillator strengths were computed, and their uncertainties were estimated to belong to the following NIST ASD classes: four in AA , 12 in A+, five in A, 13 in B+, six in B, and four in C+ with AA ≤ 1%, A+ ≤ 2%, A ≤ 3%, B+ ≤ 7%, B ≤ 10%, C+ ≤ 18%. The remaining transitions, mainly weak transitions involving the 4d<sup>9</sup>5s<sup>2</sup> states, were estimated to be in the E class >50%. The computed lifetimes from both the MCDHF and RCC methods are in good mutual agreement and mostly fall within the error bars of available experimental values from laser-induced fluorescence measurements. The 4d<sup>9</sup>5s<sup>2</sup> <sup>2</sup>D<sub>5/2</sub> metastable state, important for establishing the ionization balance, decay through an E2 transition to the ground state. The calculated lifetime is 163 ms. The computed hyperfine interaction constants from the MCDHF and RCC methods are in good agreement and compare well with the scattered experimental constants.</p>