Local Dense Structural Heterogeneities in Liquid Water from Ambient to 300 MPa Pressure: Evidence for Multiple Liquid-Liquid Transitions

• Published in: Chemphyschem 2004-09, Vol.5 (9), p.1398-1404
• Main Authors: Khoshtariya, Dimitri E., Zahl, Achim, Dolidze, Tina D., Neubrand, Anton, van Eldik, Rudi
• Format: Article
• Language: English
• Subjects: Condensed matter: structure, mechanical and thermal properties; dense clusters; Exact sciences and technology; high pressure; hydrogen bonding; liquids; Molecular liquids; Physics; Structure of solids and liquids; crystallography; Studies of specific liquid structures; vibrational spectroscopy; water
• ISSN: 1439-4235; 1439-7641
• DOI: 10.1002/cphc.200400219

Difference and double‐difference near‐infrared DO–D and HO–H stretching overtone (2νOD and 2νOH) spectroscopy and a rigorous (physically substantiated) band deconvolution technique were applied to reveal three different kinds of inherent (interstitial) structures of liquid water, which determine its high density (compared to ice Ih under ambient conditions), its compressibility (under hydrostatic pressure, up to 300 MPa), and its high fragility (manifested under temperature variation). Our data processing allowed the rigorous discrimination of up to six vibrational components. On the basis of an extensive comparative analysis combined with available structural data (X‐ray and neutron scattering) and molecular dynamics (MD) simulations for liquid water, as well as with experimental and computed data for small non‐tetrahedrally arranged water clusters, the major four components could be ascribed to: i) The basic Ih icelike substructure; ii) the temperature‐dependent remote interstitial “defects” due to tetrahedral displacements (primarily responsible for transport properties); iii) the interstitial “defects” most probably arranged in quasiplanar noncyclic tetramers (totally absent in the ice structure); and iv) the interstitial “defects” formed with increasing pressure, probably arranged in cubic water octamers and composed of two pairs of noncyclic and cyclic tetramer fragments. The latter structures include, essentially, bent hydrogen bonds stabilized by resonance effects. Don't crack under pressure! The graphic shows a water cubic octamer (in red) fitted to the hexagonal quasicrystalline (Ih icelike) lattice (in black). Note an almost ideal compatibility between the basic (“water II”) and the pressure‐induced (dense) substructures.