The Editors at The Journal of Chemical Physics facilitate publication of the most innovative and influential articles in the field of Chemical Physics each year. In a recent edition, the Editors selected a few of the many notable JCP articles published in 2009 that present ground-breaking research and amongst them is a paper by LCN’s Prof. John Finney.
One of the intriguing properties of water ice is its ability to exist not only in a number of crystalline phases but also in a number of amorphous forms of different densities. The existence of these “polyamorphs” has become a subject of considerable debate within the context of the general understanding of water, and particularly its liquid state.
A recent computer simulation study raised the tantalizing possibility of a second distinct low density form of amorphous ice. The existence of such a second low-density form would challenge the prevailing experimental view of one low density amorphous structure which is thought to be the metastable minimum structure.
Using isotope substitution neutron scattering at the ISIS facility, the experimental results do indeed indicate that there exist at least two structural states of low density amorphous ice; the primary difference in the structures occurs on an extended length scale in the hydrogen bonded network of molecules. However, the data clearly show that these two low-density forms are not distinct forms of ice in the way that the low density forms differ from the higher density ones; rather, they are two closely related, but kinetically trapped forms of what could be considered the true metastable low density amorphous ice.
In terms of an energy landscape that is explored during the transition from the high density structures to the lower density state, the two structures can be considered representatives of related but different energy minima in the general LDA energy basin.
John’s publication is featured under the section ‘Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation’. To access this go to http://jcp.aip.org/jcp/editors_choices_2009, click on Condensed Phase Dynamics, Structure, and Thermodynamics: Spectroscopy, Reactions, and Relaxation, and it's the 4th paper down.
Relaxation effects in low density amorphous ice: Two distinct structural states observed by neutron diffraction
K. Winkel, D. T. Bowron, T. Loerting, E. Mayer, and J. L. Finney
J. Chem. Phys. 130, 204502 (2009)