Water beyond its boiling temperature has been investigated by numerous
theoretical and experimental tools including classical and quantum simulations,
Neutron Scattering, Nuclear Magnetic Resonance, Infra−Red, and a more recent
Tetrahertz Vibrational−Rotational−Tunnelling spectroscopic technique. Water becomes
Super Critical Water (SCW) when it reaches temperature 647 K with critical pressure
and density at which vapour and liquid phases coexist. SCW has been found to have
exceptional properties such that many chemical reactions can be efficiently carried out
without the presence of catalysts, and hence is considered as a better alternative to
many of the traditional reagents, which are currently being used in organic synthesis. It
is also effective in biofuel production and in burying toxic waste products by
converting them to water and CO2. Simulations and experiments point into dramatic
changes in the intermolecular structure of water at elevated temperatures signalled by
depletion of tetrahedral hydrogen bonding network, which gives rise to higher
population of water clusters than found in ambient water, with varying size and
geometry. Cyclic water isomers are found to be stable up to clusters containing five
water molecules, whereas three dimensional cage structures are found to be stable in
higher analogues. Density along with temperature plays a vital role in determining
diffusive properties of SCW. It has been demonstrated by numerous experiments and
computer simulations that a proportional increase in hydrogen bonding is observed as
density increases. On the contrary, diffusive motion of water molecules is retarded
upon a hike in density.
Keywords: Ab-initio, Aldol, Benzamide, Cannizzaro, Density, Dimers, Friedel
Craft, Hexamer, IR, NMR, Pentamer, SCW, Tetrahedral, Tetramer, Trimer, Water
Clusters.
