Bull, C. L.

Loveday, J. S.

Stinton, G.

Wilson, C. W.

C. W. Wilson

C. L. Bull

G. Stinton

J. S. Loveday

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The Journal of Chemical Physics

Pressure-induced dehydration and the structure of ammonia hemihydrate-II

Wilson CW

Bull CL

Stinton G

Loveday JS

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The structure of the crystalline ammonia-bearing phase formed when ammonia monohydrate liquid is compressed to 3.5(1) GPa at ambient temperature has been solved from a combination of synchrotron x-ray single-crystal and neutron powder-diffraction studies. The solution reveals that rather than having the ammonia monohydrate (AMH) composition as had been previously thought, the structure has an ammonia hemihydrate composition. The structure is monoclinic with spacegroup P2(1)/c and lattice parameters a = 3.3584(5) angstrom, b = 9.215(1) angstrom, c = 8.933(1) angstrom and beta = 94.331(8)degrees at 3.5(1) GPa. The atomic arrangement has a crowned hexagonal arrangement and is a layered structure with long N-D center dot center dot center dot N hydrogen bonds linking the layers. The existence of pressure-induced dehydration of AMH may have important consequences for the behaviour and differentiation of icy planets and satellites. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.3686870]</p

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Pressure-induced dehydration and the structure of ammonia hemihydrate-II

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