10.1021/acs.jpcb.7b09688.s001 Christoph J. Sahle Christoph J. Sahle Johannes Niskanen Johannes Niskanen Christian Schmidt Christian Schmidt Johannes Stefanski Johannes Stefanski Keith Gilmore Keith Gilmore Yury Forov Yury Forov Sandro Jahn Sandro Jahn Max Wilke Max Wilke Christian Sternemann Christian Sternemann Cation Hydration in Supercritical NaOH and HCl Aqueous Solutions American Chemical Society 2017 fingerprinting analysis NaOH molecules HCl Aqueous Solutions hydrogen-bonding topology oxygen atoms ab initio simulation results Experimental nonresonant X-ray Raman Cation Hydration Supercritical NaOH oxygen K-edge show water structure solution dynamics simulations core-level spectra hydration shells 2017-11-21 00:00:00 Journal contribution https://acs.figshare.com/articles/journal_contribution/Cation_Hydration_in_Supercritical_NaOH_and_HCl_Aqueous_Solutions/5682688 We present a study of the local atomic environment of the oxygen atoms in the aqueous solutions of NaOH and HCl under simultaneous high-temperature and high-pressure conditions. Experimental nonresonant X-ray Raman scattering core-level spectra at the oxygen K-edge show systematic changes as a function of temperature and pressure. These systematic changes are distinct for the two different solutes and are described well by calculations within the Betheā€“Salpeter formalism for snapshots from ab initio molecular dynamics simulations. The agreement between experimental and simulation results allows us to use the computations for a detailed fingerprinting analysis in an effort to elucidate the local atomic structure and hydrogen-bonding topology in these relevant solutions. We observe that both electrolytes, especially NaOH, enhance hydrogen bonding and tetrahedrality in the water structure at supercritical conditions, in particular in the vicinity of the hydration shells. This effect is accompanied with the association of the HCl and NaOH molecules at elevated temperatures.