arXiv subjects

Hans Ågren

Publications and source records attributed to Hans Ågren.

6 recordsLinked to original sources

arXiv2026

Core-valence double ionization of SF6 involving S2p, F1s and S1s inner shells

Core-valence double ionization electron spectra near the S2p, F1s and S1s edges of SF6 are presented, analyzed and compared with conventional valence photoelectron spectra and quantum chemical calculations. The core-valence spectra are energetically stretched out, revealing salient structures between 15 and 40 eV that are sufficiently separated for molecular orbital analysis. The spectra offer new insights into the electronic structure, showing that the core hole substantially rearranges the molecular orbital order. This effect can be traced to orbital localization and nodal structure, as well as to valence-to-core penetration. The singlet and triplet splittings of the dicationic states progressively decrease in all three core-valence spectra towards deeper core levels, with larger splittings for S2p than S1s, reflecting greater valence-to-core penetration and exchange interaction for S2p. By large, the MO interpretation holds in frozen or self-consistent-field representations, except for the inner parts of the F1s spectra, which require analysis in terms of MO breakdown effects. An intensity model for CV spectra is derived using an independent-channel approach, where primary core ionization is treated by dipolar coupling to a continuum and the valence electron is promoted to a second continuum through shake-off. Full spin coupling and spin selectivity between the discrete doubly ionized states and the two continuum electrons are maintained. The primary molecular photoelectron intensity is expressed as a weighted sum of atomic subshell cross sections using a one-center atomic orbital projection of the relevant molecular orbital. The calculated spectra agree well with experiment and allow detailed assignment. In particular, symmetry breaking at the F1s core-ionization site is identified and discussed.

physics.chem-ph↗

arXiv2025

Interaction of Polymer of Intrinsic Microporosity PIM-1 with explosive analytes at the molecular level: Combined experiment and computational modelling

This work investigates the molecular-level interactions of a fluorescent microporous polymer (PIM-1) with nitroaromatic explosives, in the context of thin film explosive sensors. Thin films of the PIM-1 were exposed to 2,4-dinitrotoluene (DNT) and 2,4,6-trinitrotoluene (TNT), and their steady-state absorption and emission spectra measured. For comparison, the response of PIM-1 to non-explosive molecules such as benzene (BN) was also explored. Complementary electronic-structure calculations were used to predict absorption and emission spectra and to determine binding energies for the PIM-1-analyte complexes. The calculations agree well with experiment and reveal that association of nitroaromatic analyte molecules with PIM-1 alters the energy levels and the arrangements of frontier orbitals, indicating significant molecular interactions. Calculations show that the electronic properties and photo-excited electron transfer can be described by interaction with a single repeat unit of the polymer. The molecular binding, however, involves interaction with at least three repeat units, with the DNT or TNT molecule binding into a pocket in the contorted structure of the microporous polymer. Together, the experimental and theoretical results demonstrate that PIM-1 is a promising platform for selective nitroaromatic detection and provide molecular design principles that could improve sensitivity and selectivity in future sensor materials.

physics.chem-ph↗

arXiv2025

Intermolecular Radiative Decay: A non-local decay mechanism providing an insider's view of the solvation shell

Aqueous solutions are crucial in chemistry, biology, environmental science, and technology. The chemistry of solutes is influenced by the surrounding solvation shell of water molecules, which have different chemical properties than bulk water due to their different electronic and geometric structure. It is an experimental challenge to selectively investigate this property-determining electronic and geometric structure. Here, we report experimental results on a novel non-local X-ray emission process, Intermolecular Radiative Decay (IRD), for the prototypical ions Na$^{+}$ and Mg$^{2+}$ in water. We show that, in IRD, an electron from the solvation shell fills a core hole in the solute, and the released energy is emitted as an X-ray photon. We analyze the underlying mechanism using theoretical calculations, and show how IRD will allow us to meet the challenge of chemically selective probing of solvation shells from within.

physics.chem-ph↗

arXiv2020

An atomistic description of alloys and core shells nanoparticles

Using the extended discrete interaction model we investigate the tuneabilty of surface plasmon resonance in alloys and core-shell nanoparticles made from silver and gold. We show that the surface plasmon resonance of these alloys and core-shell particles to a large extent follow Vegard's law irrespective of the geometry of the nanoparticle. We show the evolution of the polarizability with size and demonstrate the highly non-linear behaviour of the polarizability with the ratio of the constituents and geometry in alloys and core-shell nanoparticles, with the exception for nanorod alloys. A thorough statistical investigation reveals that there is only a small dependence of the surface plasmon resonance on atomic arrangement and exact distribution in a nanoparticle and that the standard deviation decrease rapidly with the size of the nanoparticles. The physical reasoning for the random distribution algorithm for alloys in discrete interaction models is explained in details and verified by the statistical analysis.

physics.optics↗

arXiv2017

Dirac magnons in honeycomb ferromagnets

The discovery of the Dirac electron dispersion in graphene led to the question of the Dirac cone stability with respect to interactions. Coulomb interactions between electrons were shown to induce a logarithmic renormalization of the Dirac dispersion. With a rapid expansion of the list of compounds and quasiparticle bands with linear band touching, the concept of bosonic Dirac materials has emerged. We consider a specific case of ferromagnets consisting of the Van der Waals-bonded stacks of honeycomb layers, e.g chromium trihalides CrX3 (X = F, Cl, Br and I), that display two spin wave modes with energy dispersion similar to that for the electrons in graphene. At the single particle level, these materials resemble their fermionic counterparts. However, how different particle statistics and interactions affect the stability of Dirac cones has yet to be determined. To address the role of interacting Dirac magnons, we expand the theory of ferromagnets beyond the standard Dyson theory to a case of non-Bravais honeycomb layers. We demonstrate that magnon-magnon interactions lead to a significant momentum-dependent renormalization of the bare band structure in addition to strongly momentum-dependent magnon lifetimes. We show that our theory qualitatively accounts for hitherto unexplained anomalies in a nearly half century old magnetic neutron scattering data for CrBr3. We also show that honeycomb ferromagnets display dispersive surface and edge states, unlike their electronic analogs.

cond-mat.mtrl-sci↗

arXiv2016

Landau-like states in neutral particles

We show the emergence of a new type of dispersion relation for neutral atoms with an interesting similarity with the spectrum of 2-dimensional electrons in an applied perpendicular constant magnetic field. These neutral atoms can be confined in toroidal optical traps and give quasi Landau spectra. In strong contrast to the equi-distant infinitely degenerate Landau levels for charged particles, the spectral gap for such 2-dimensional neutral particles increases in particular electric field configurations. The idea in the paper is motivated by the development in cold atom experiments and builds on the seminal paper of Aharonov and Casher.

quant-ph↗