Melting and dissociation of ammonia at high pressure and high temperature

J. G. O. Ojwang, R. Stewart McWilliams, Xuezhi Ke, Alexander F. Goncharov*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

Abstract

Raman spectroscopy and synchrotron x-ray diffraction measurements of ammonia (NH3) in laser-heated diamond anvil cells, at pressures up to 60 GPa and temperatures up to 2500 K, reveal that the melting line exhibits a maximum near 37 GPa and intermolecular proton fluctuations substantially increase in the fluid with pressure. We find that NH3 is chemically unstable at high pressures, partially dissociating into N-2 and H-2. Ab initio calculations performed in this work show that this process is thermodynamically driven. The chemical reactivity dramatically increases at high temperature (in the fluid phase at T > 1700 K) almost independent of pressure. Quenched from these high temperature conditions, NH3 exhibits structural differences from known solid phases. We argue that chemical reactivity of NH3 competes with the theoretically predicted dynamic dissociation and ionization. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4742340]

Original languageEnglish
Article number064507
Number of pages8
JournalThe Journal of Chemical Physics
Volume137
Issue number6
DOIs
Publication statusPublished - 14 Aug 2012

Keywords

  • TOTAL-ENERGY CALCULATIONS
  • AUGMENTED-WAVE METHOD
  • ROOM-TEMPERATURE
  • RAMAN-SCATTERING
  • PLANETARY ICES
  • ELECTRON-GAS
  • BASIS-SET
  • URANUS
  • GPA
  • INTERIOR

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