National and international collaboration: Felix Hoffmann,‡ Gül Bekçioğlu,‡ Daniel Sebastiani,‡ Wilson Quevedo,+ Markus Kubin,+ Philippe Wernet+, M. Odelius,* Subhajyoti Chaudhuri,# Atanu Acharya,#Victor S. Batista,# Dina Pines,† Ehud Pines†
‡: Institut für Chemie, Martin-Luther-Universität Halle-Wittenberg, Von-Danckelmann-Platz 4, 06120 Halle (Saale), Germany
+: Ultrafast X-Ray Science Group, Helmholtz-Zentrum Berlin, BESSY II, Albert-Einstein-Str. 15, D-12489 Berlin, Germany
*: Department of Physics, Stockholm Universitet, Stockholm, Sweden
†: Department of Chemistry, Ben Gurion University of the Negev, Beer-Sheva, 84105 Israel
#: Department of Chemistry, Yale University, P.O. Box 208107, New Haven, Connecticut 06520-8107, United States of America
Photoacids are used to investigate the elementary steps in water-mediated proton transfer reactions. IR and soft-x-ray spectroscopy are used as local probing tools on transient vibrational and electronic structure. Femtosecond UV-pump/IR-probe spectroscopy is used to follow the response of the photoacids, hydration shell water and bases during different stages of the proton transport. Soft-x-ray spectroscopy using flatjet technology is used to explore hydrogen bonding interactions of photoacids and bases, and will be further developped as technique probing hydrogen bonding interactions on ultrafast time scales. Proton transport along hydrogen-bonded solvent bridges connecting acid and base sites of bifunctional photoacids has been studied in a combined experimental and theoretical approach since 2015. This research is in part funded by a DFG Normalverfahren NI 492/13-1 /SE 1008/11-1 jointly with D. Sebastiani (2015-2017). Since 2018 third party funding comes from an ERC Advanced Grant (XRayProton, Nibbering, 2018-2023).
3-1 Proton transport along solvent bridges
1. 7-hydroxyquinoline (7HQ), where solvent bridges connecting proton donating and accepting groups are at a well-defined distance of three solvent molecules, exhibits both photoacid and photobase properties through the 2-naphthol and quinoline moieties.
2. Femtosecond UV-IR pump-probe spectroscopy monitors the population kinetics of the differently charged forms of 7HQ.
3. Distinct difference in lifetimes of 7HQ N*, C* and A*, all eventually reacting towards Z*.
4. 7HQ relative importance reaction pathway assessment.
3-2 Soft-X-ray spectroscopy of acids and bases
5. Flatjet technology for soft-X-ray spectroscopy of liquids and solutions.
6. N K-edge spectroscopy of aqueous NH3 and NH4+.
7. Graphical presentation of orbitals reached upon N 1s excitation of aqueous ammonia and ammonium ion.
8. N K-edge spectroscopy of alkylamines and alkylammonium ions.
9. Calculated N K-edge spectra and associated molecular orbitals reached upon N 1s excitation for the alkylamine and alkylammonium ion series.
10. Flatjet technology has been applied in measurements on 3d L-edge transitions of metal-ion complexes in ethanol solution, probing electronic structure and spin densities of the metal-ligand bonding.