title: Investigation of the Ionic Hydration in Aqueous Salt Solutions by Soft X-ray Emission Spectroscopy.
abstract: Understanding the molecular structure of the hydration shells and their impact on the hydrogen bond (HB) network of water in aqueous salt solutions is a fundamentally important and technically relevant question. In the present work, such hydration effects were studied for a series of representative salt solutions (NaCl, KCl, CaCl2, MgCl2, and KBr) by soft X-ray emission spectroscopy (XES) and resonant inelastic soft X-ray scattering (RIXS). The oxygen K-edge XES spectra could be described with three components, attributed to initial state HB configurations in pure water, water molecules that have undergone an ultrafast dissociation initiated by the X-ray excitation, and water molecules in contact with salt ions. The behavior of the individual components, as well as the spectral shape of the latter component, has been analyzed in detail. In view of the role of ions in such effects as protein denaturation (i.e., the Hofmeister series), we discuss the ion-specific nature of the hydration shells and find that the results point to a predominant role of anions as compared to cations. Furthermore, we observe a concentration-dependent suppression of ultrafast dissociation in all salt solutions, associated with a significant distortion of intact HB configurations of water molecules facilitating such a dissociation.
authors.affiliation: Angewandte Physikalische Chemie, Universität Heidelberg , Im Neuenheimer Feld 253, 69120 Heidelberg, Germany.
authors.forename: Y L
authors.initials: YL
authors.lastname: Jeyachandran
authors.affiliation: Experimentelle Physik VII, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Meyer
authors.affiliation: Experimentelle Physik VII, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.|Institute for Photon Science and Synchrotron Radiation (IPS), Karlsruhe Institute of Technology (KIT) , Hermann-v.-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.
authors.forename: A
authors.initials: A
authors.lastname: Benkert
authors.affiliation: Renewable Energy, Helmholtz-Zentrum Berlin für Materialien und Energie GmbH , Hahn-Meitner-Platz 1, 14109 Berlin, Germany.|Institute für Physik und Chemie, Brandenburgische Technische Universität Cottbus-Senftenberg , Platz der Deutschen Einheit 1, 03046 Cottbus, Germany.|Department of Chemistry and Biochemistry, University of Nevada, Las Vegas (UNLV) , 4505 Maryland Parkway, Las Vegas, Nevada 89154-4003, United States.
authors.forename: M
authors.initials: M
authors.lastname: Bär
authors.affiliation: Department of Chemistry and Biochemistry, University of Nevada, Las Vegas (UNLV) , 4505 Maryland Parkway, Las Vegas, Nevada 89154-4003, United States.
authors.forename: M
authors.initials: M
authors.lastname: Blum
authors.affiliation: Advanced Light Source (ALS), Lawrence Berkeley National Laboratory , 1 Cyclotron Road, Berkeley, California 94720, United States.
authors.forename: W
authors.initials: W
authors.lastname: Yang
authors.affiliation: Experimentelle Physik VII, Universität Würzburg, Am Hubland, 97074 Würzburg, Germany.
authors.forename: F
authors.initials: F
authors.lastname: Reinert
authors.affiliation: Institute for Photon Science and Synchrotron Radiation (IPS), Karlsruhe Institute of Technology (KIT) , Hermann-v.-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.|Department of Chemistry and Biochemistry, University of Nevada, Las Vegas (UNLV) , 4505 Maryland Parkway, Las Vegas, Nevada 89154-4003, United States.|Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe Institute of Technology (KIT) , Engesserstrasse 18/20, 76028 Karlsruhe, Germany.
authors.forename: C
authors.initials: C
authors.lastname: Heske
authors.affiliation: Institute for Photon Science and Synchrotron Radiation (IPS), Karlsruhe Institute of Technology (KIT) , Hermann-v.-Helmholtz-Platz 1, 76344 Eggenstein-Leopoldshafen, Germany.|Department of Chemistry and Biochemistry, University of Nevada, Las Vegas (UNLV) , 4505 Maryland Parkway, Las Vegas, Nevada 89154-4003, United States.|Institute for Chemical Technology and Polymer Chemistry (ITCP), Karlsruhe Institute of Technology (KIT) , Engesserstrasse 18/20, 76028 Karlsruhe, Germany.
authors.forename: L
authors.initials: L
authors.lastname: Weinhardt
authors.affiliation: Angewandte Physikalische Chemie, Universität Heidelberg , Im Neuenheimer Feld 253, 69120 Heidelberg, Germany.
authors.forename: M
authors.initials: M
authors.lastname: Zharnikov