The structural memory of water persists on a picosecond timescale

A team of scientists from the Max Planck Institute for Polymer Research (MPI-P) in Mainz, Germany and FOM Institute AMOLF in the Netherlands has characterized the local structural dynamics of liquid water, i.e. how quickly water molecules change their binding state. Using innovative ultrafast vibrational spectroscopies, the researchers show why liquid water is unique when compared to most other molecular liquids. This study has recently been published in the scientific journal Nature Communications.

With the help of a novel combination of ultrafast laser experiments, the scientists found that local structures persist in water for longer than a picosecond, a picosecond (ps) being one thousandth of one billionth of a second (10exp-12  s). This observation changes the general perception of water as a solvent. Water is a very special liquid with extremely fast dynamics. Water molecules wiggle and jiggle on sub-picosecond timescales, which make them undistinguishable on this timescale. While the existence of very short-lived local structures — e.g. two water molecules that are very close to one another, or are very far apart from each other — is known to occur, it was commonly believed that they lose the memory of their local structure within less than 0.1 picoseconds.

The proof for relatively long-lived local structures in liquid water was obtained by measuring the vibrations of the Oxygen-Hydrogen (O-H) bonds in water. For this purpose the team of scientists used ultrafast infrared spectroscopy, particularly focusing on water molecules that are weakly (or strongly) hydrogen-bonded to their neighboring water molecules. The scientists found that the vibrations live much longer (up to about 1 ps) for water molecules with a large separation, than for those that are very close (down to 0.2 ps). In other words, the weakly bound water molecules remain weakly bound for a remarkably long time.

Sourced through Scoop.it from: scienceyear.net

See on Scoop.itAgroSup Dijon Veille Scientifique AgroAlimentaire – Agronomie


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