arXiv subjects

Giorgio Visentin

Publications and source records attributed to Giorgio Visentin.

7 recordsLinked to original sources

arXiv2026

Extracting inter-nuclear distances in the oxygen molecule interacting with an XFEL-pulse: a fundamental system for understanding Coulomb explosion imaging

We investigate the interaction of O$_{2}$ with an X-ray Free Electron laser (XFEL) pulse of short duration. We consider a photon energy of 570 eV, which allows for the formation of molecular states with up to two core holes. We compute the sum of the final kinetic energies, i.e. the kinetic energy release (KER) of the atomic fragments for different fragmentation channels. We demonstrate that with the knowledge of the potential energy curves the equilibrium inter-nuclear distance of O$_{2}$ is best extracted from the O$^{+}$+O$^{+}$ channel and not from higher-charged channels such as O$^{2+}$+O$^{2+}$. This challenges our current understanding of Coulomb explosion imaging, where from just applying quasi-classical dynamics one expects that the equilibrium inter-nuclear distance of molecules is best extracted from higher-charged fragmentation channels. On the other hand, we show that the KER of the O$^{+}$+O$^{+}$ channel is inconsistent with the one obtained by just calculating the Coulomb repulsion of the atomic fragments resulting from molecular dissociation.

physics.atom-ph↗

arXiv2025

Configuration-interaction calculations with density-functional theory molecular orbitals for modeling valence- and core-excited states in molecules

We investigate configuration-interaction (CI) calculations on a basis of molecular orbitals generated by preliminary density-functional theory (DFT) calculations. We use this CI/DFT framework to improve the modeling of core-excited states by exploiting the flexibility and account for electron correlation of DFT orbitals compared to the canonical Hartree-Fock analogs. We assess the performance of our approach on the valence- and core-excited electronic states of three molecules with increasing levels of electron-correlation complexity: the singly bonded CH4, doubly bonded CO2, and triply bonded N2. For molecules with strong electron correlation effects, such as CO2 and N2, the inclusion of double excitations is important to model the core-hole excited states with reasonable accuracy. CI/DFT outperforms standard single-reference CI on Hartree-Fock molecular orbitals and competes with multi-reference CI calculations with multi-configuration self-consistent field orbitals in the modeling of molecules with strong electron-correlation effects, but weak multi-reference nature of their wave function such as CO2. In contrast, the choice of the molecular-orbital basis is irrelevant when modeling systems with negligible electron-correlation effects like CH4 or important multi-reference nature of their wave function like N2.

physics.chem-ph↗

arXiv2024

Chemical Evolution of R-process Elements in Stars (CERES): IV. An observational run-up of the third r-process peak with Hf, Os, Ir, and Pt

The third r-process peak (Os, Ir, Pt) is poorly understood due to observational challenges, with spectral lines located in the blue or near-ultraviolet region of stellar spectra. These challenges need to be overcome for a better understanding of the r-process in a broader context. To understand how the abundances of the third r-process peak are synthesised and evolve in the Universe, a homogeneous chemical analysis of metal-poor stars using high quality data observed in the blue region of the electromagnetic spectrum (< 400 nm) is necessary. We provide a homogeneous set of abundances for the third r-process peak (Os, Ir, Pt) and Hf, increasing by up to one order of magnitude their availability in the literature. A classical 1D, local thermodynamic equilibrium (LTE) analysis of four elements (Hf, Os, Ir, Pt) is performed, using ATLAS model atmospheres to fit synthetic spectra in high resolution (> 40,000), high signal-to-noise ratio, of 52 red giants observed with UVES/VLT. Due to the heavy line blending involved, a careful determination of upper limits and uncertainties is done. The observational results are compared with state-of-the-art nucleosynthesis models. Our sample displays larger abundances of Ir (Z=77) in comparison to Os (Z=76), which have been measured in a few stars in the past. The results also suggest decoupling between abundances of third r-process peak elements with respect to Eu (rare earth element) in Eu-poor stars. This seems to contradict a co-production scenario of Eu and the third r-process peak elements Os, Ir, and Pt in the progenitors of these objects. Our results are challenging to explain from the nucleosynthetic point of view: the observationally derived abundances indicate the need for an additional early, primary formation channel (or a non-robust r-process).

astro-ph.SR↗

arXiv2024

Laser Resonance Chromatography of $^{229}$Th$^{3+}$ in He: an ab initio investigation

We propose a laser resonance chromatography (LRC) experiment on $^{229}$Th$^{3+}$, with the goal of detecting the ion's electronic ground $5f$ $^2$F$_{5/2}$ state and metastable $7s$ $^2$S$_{1/2}$ state by means of their ion mobilities. To this end, we first model the ion-neutral interaction potentials for the two electronic states with a relativistic Fock space coupled cluster method and complete basis-set extrapolation scheme. The interaction potentials are used to simulate the state-specific reduced ion mobilities in terms of the operating temperature and the external electric field. The ion mobilities differ by more than 7% at 300 K and moderate field strengths; thus, separation of the $^{229}$Th$^{3+}$ metastable state lies within the reach of LRC experiments targeting optical probing and monitoring of the nuclear clock transition in this isotope.

physics.atom-ph↗

arXiv2024

Transport property predictions for laser resonance chromatography on Rf$^+$ (Z = 104)

We propose a theoretically designed laser resonance chromatography (LRC) experiment on Rf$^+$ (Z = 104) drifting in He buffer gas. To this end, we first developed a four-level rate equation model that simulates the optical pumping of Rf$^+$ from its ground state, $^2$D$_{3/2}$ (7s$^2$6d$^1$), to the metastable $^4$F$_{3/2}$ (7s$^1$6d$^2$) state via laser resonant excitation of the intermediate $^4$F$_{3/2}$ (7s$^1$6d$^1$7p$^1$) state prior to electronic state chromatography. This model predicts a 93% pumping efficiency that suffices to enable efficient laser resonance chromatography of this ion. We then performed accurate relativistic Multi-Reference Configuration-Interaction (MRCI) calculations to model the interaction of Rf$^+$ with He in the ground $^2$D$_{3/2}$ (7s$^2$6d$^1$), low-lying $^2$D$_{5/2}$ (7s$^2$6d$^1$), and metastable $^4$F$_{3/2}$ (7s$^1$6d$^2$) states. These ion-atom interaction potentials were used to calculate the state-specific ion mobilities. For gas temperatures above 100 K and small applied electric fields, the reduced ion mobilities of the ground and metastable states differ significantly. In particular, at room temperature the difference between the reduced ion mobilities of these states is larger than 11%, and as such sufficiently large to ensure LRC of this ion.

physics.atom-ph↗

arXiv2021

Reexamination of the ground state Born-Oppenheimer Yb$_2$ potential

The precision of the photoassociation spectroscopy of Yb dimer in degenerate gases is enough to improve the constraints on the new short-range gravity-like forces if the theoretical knowledge of the Born-Oppenheimer interatomic potential and non-Born-Oppenheimer interactions is refined [M. Borkowski et al. Sci. Rep. A {\bf 9}, 14807 (2019)]. The ground-state interaction potential of ytterbium dimer is investigated at the eXact 2-component core-correlated CCSD(T) level of {\it ab initio} theory in the complete basis set limit with extensive augmentation by diffuse functions. For the small basis set the comparison is made with the four-component relativistic finite-nuclei CCSD(T) calculations to identify the contraction of the dimer bond length as the main unrecoverable consequence of the scalar-relativistic approximation. Empirical constraint on the number of bound vibrational energy levels of the $^{174}$Yb$_2$ dimer is accounted for by representing the global {\it ab initio}-based Born-Oppenheimer potential with the model semianalytical function containing the scale and shift parameters. The results support the previous evaluation of the Yb dimer potentials from the photoassociation spectroscopy data and provide an accurate and flexible reference for future refinement of the constraints on the short-range gravity-like forces by ultracold atomic spectroscopy.

physics.atom-ph↗

arXiv2020

Mobility of the Singly-Charged Lanthanide and Actinide Cations: Trends and Perspectives

The current status of gaseous transport studies of the singly-charged lanthanide and actinide ions is reviewed in light of potential applications to superheavy ions. The measurements and calculations for the mobility of lanthanide ions in He and Ar agree well, and they are remarkably sensitive to the electronic configuration of the ion, namely, whether the outer electronic shells are 6s, 5d6s or 6s$^2$. The previous theoretical work is extended here to ions of the actinide family with zero electron orbital momentum: Ac$^+$ (7s$^2$, $^1$S), Am$^+$ (5f$^7$7s $^9$S$^\circ$), Cm$^+$ (5f$^7$7s$^2$ $^8$S$^\circ$), No$^+$ (5f$^{14}$7s $^2$S) and Lr$^+$ (5f$^{14}$7s$^2$ $^1$S). The calculations reveal large systematic differences in the mobilities of the 7s and 7s$^2$ groups of ions and other similarities with their lanthanide analogs. The correlation of ion-neutral interaction potentials and mobility variations with spatial parameters of the electron distributions in the bare ions is explored through the ionic radii concept. While the qualitative trends found for interaction potentials and mobilities render them appealing for superheavy ion research, lack of experimental data and limitations of the scalar relativistic ab initio approaches in use make further efforts necessary to bring the transport measurements into the inventory of techniques operating in ''one atom at a time'' mode.

physics.atom-ph↗