# Research Group HELIXS

## Collection by Mikko Hakala

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Recent publications and activities of the HELIXS group (helixs.physics.helsinki.fi). Department of Physics, University of Helsinki. HELIXS - Helsinki Electronic Structure and Inelastic X-ray Scattering. www.twitter.com/helixsfi See all the publications at helixs.physics.helsinki.fi/index.php/research/publications

Resources and links related to X-ray free electron lasers, currently operational and the ones under construction. Figure copyright: European XFEL (Design: Marc Hermann, tricklabor) www.xfel.eu.

We report high-resolution x-ray Raman scattering studies of high-order multipole spectra of rare earth excitations (the absorption edge) in nanoparticles of the phosphates LaPO4, CePO4, PrPO4, and NdPO4. We also present corresponding data for La excitations (the edge) in LaPO4. The results are compared with those from calculations by atomic multiplet theory and for the dipole contribution to the La transition from a calculation using time-dependent density functional theory (TDLDA)…

We characterize experimentally and theoretically the collective electronic excitations in two prototypical layered transition-metal dichalcogenides, ${\mathrm{NbSe}}_{2}$ and ${\mathrm{Cu}}_{0.2}{\mathrm{NbS}}_{2}$. The energy- and momentum-dependent dynamical structure factor was measured by inelastic x-ray scattering (IXS) spectroscopy and simulated by time-dependent density-functional theory. We find good agreement between theory and experiment, provided that Nb semicore states are taken…

IXS 2015

A classic example of solid-state topochemical reactions is the ultraviolet-light induced photodimerization of α-trans-cinnamic acid (CA). Here, we report the first observation of an X-ray-induced dimerization of CA and monitor it in situ using nonresonant inelastic X-ray scattering spectroscopy (NRIXS). The time-evolution of the carbon core-electron excitation spectra shows the effects of two X-ray induced reactions: dimerization on a short time-scale and disintegration on a long time-scale…

Finnish Synchrotron Radiation Users' Organization, Suomen synkrotronisäteilyn käyttäjien yhdistys, FSRUO

New B.Sc. thesis in the HELIXS research group Oct 2015: Functional multilayer crystal structures - helixs.physics.helsinki.fi

Hydration of sulfuric acid plays a key role in new-particle formation in the atmosphere. It has been recently proposed that proton dynamics is crucial in the stabilization of these clusters. One key question is how water molecules mediate proton transfer from sulfuric acid, and hence how the deprotonation state of the acid molecule behaves as a function concentration. We address the proton transfer in aqueous sulfuric acid with O K edge and S L edge core-excitation spectra recorded using…

Matemaattis-luonnontieteellisessä tiedekunnassa tehdään kansainvälisesti korkeatasoista tutkimusta. Opetusta kehittävät ja antavat eturivin luonnontieteilijät.

Polarization dependent hard X-ray photoemission experiments for solids: Efficiency and limits for unraveling the orbital character of the valence band - J. Weinen et al. - Journal of Electron Spectroscopy and Related Phenomena, Volume 198, January 2015, Pages 6–11

Using ethanol–water solutions as illustration, we demonstrate the capability of the hybrid quantum mechanics/molecular mechanics (QM/MM) paradigm to simulate core photoelectron spectroscopy: the binding energies and the chemical shifts. An integrated approach with QM/MM binding energy calculations coupled to preceding molecular dynamics sampling is adopted to generate binding energies averaged over the solute–solvent configurations available at a particular temperature and pressure and thus…