title: Ammonia as a case study for the spontaneous ionization of a simple hydrogen-bonded compound.
abstract: Modern ab initio calculations predict ionic and superionic states in highly compressed water and ammonia. The prediction apparently contradicts state-of-the-art experimentally established phase diagrams overwhelmingly dominated by molecular phases. Here we present experimental evidence that the threshold pressure of ~120 GPa induces in molecular ammonia the process of autoionization to yet experimentally unknown ionic compound--ammonium amide. Our supplementary theoretical simulations provide valuable insight into the mechanism of autoionization showing no hydrogen bond symmetrization along the transformation path, a remarkably small energy barrier between competing phases and the impact of structural rearrangement contribution on the overall conversion rate. This discovery is bridging theory and experiment thus opening new possibilities for studying molecular interactions in hydrogen-bonded systems. Experimental knowledge on this novel ionic phase of ammonia also provides strong motivation for reconsideration of the theory of molecular ice layers formation and dynamics in giant gas planets.
authors.affiliation: 1] Max Planck Institute for Chemistry, 55128 Mainz, Germany [2] Institute of Physical Chemistry PAS, Warsaw 01-224, Poland.
authors.forename: Taras
authors.initials: T
authors.lastname: Palasyuk
authors.affiliation: 1] Max Planck Institute for Chemistry, 55128 Mainz, Germany [2] A. V. Shubnikov Institute of Crystallography, Russian Academy of Sciences, 119333 Moscow, Russia.
authors.forename: Ivan
authors.initials: I
authors.lastname: Troyan
authors.affiliation: Max Planck Institute for Chemistry, 55128 Mainz, Germany.
authors.forename: Mikhail
authors.initials: M
authors.lastname: Eremets
authors.affiliation: Florida International University, Miami, Florida 33199, USA.
authors.forename: Vadym
authors.initials: V
authors.lastname: Drozd
authors.affiliation: Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany.
authors.forename: Sergey
authors.initials: S
authors.lastname: Medvedev
authors.affiliation: Institute of Physical Chemistry PAS, Warsaw 01-224, Poland.
authors.forename: Patryk
authors.initials: P
authors.lastname: Zaleski-Ejgierd
authors.affiliation: Institute of Physical Chemistry PAS, Warsaw 01-224, Poland.
authors.forename: Ewelina
authors.initials: E
authors.lastname: Magos-Palasyuk
authors.affiliation: Max Planck Institute for Chemistry, 55128 Mainz, Germany.
authors.forename: Hongbo
authors.initials: H
authors.lastname: Wang
authors.affiliation: 1] Lawrence Livermore National Laboratory, Livermore, California 94550, USA [2] Department of Physics, Dalhousie University, Halifax, Nova Scotia, Canada B3H3J5.
authors.forename: Stanimir A
authors.initials: SA
authors.lastname: Bonev
authors.affiliation: 1] Max Planck Institute for Polymer Research, 55128 Mainz, Germany [2].
authors.forename: Dmytro
authors.initials: D
authors.lastname: Dudenko
authors.affiliation: 1] A. V. Shubnikov Institute of Crystallography, Russian Academy of Sciences, 119333 Moscow, Russia [2] Max Planck Institute for Chemical Physics of Solids, 01187 Dresden, Germany.
authors.forename: Pavel
authors.initials: P
authors.lastname: Naumov