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Prof. Ehud Pines has Promising Answer to Centuries-Old Chemistry Question

Jul. 16, 2017

How water accommodates acids is a long-standing, centuries-old question in chemistry. The key to this question is the structure of the hydrated proton, the chemically active ingredient in acids. Acids are found everywhere and their control in nature is essential for the well being of our environment as well as our body’s health. 

Prof. Ehud​ Pines from BGU suggested a way to study the structure of strong acids in water. Teaming up with a research group at the Max-Born Institute in Berlin headed by Professor Thomas Elsasser, a clear picture of the structure of the hydrated proton of strong acids emerged by applying ultrafast vibrational spectroscopy. 

The study was published online by Science through their First Release platform late last week entitled “Large amplitude of transfer motions the hydrated proton mapped by 2-Dvibrational spectroscopy”. 

The study mapped fluctuating proton transfer motions and provides direct evidence that protons in liquid water are shared by two water molecules which keep the proton locked inside  a two-atom potential box for relatively long times that may exceed 1 picosecond. The results imply that the femtosecond large-amplitude proton movement within a particular box are 10 to 50 times faster than proton hopping to a new hydration site, the elementary charge transfer step in chemistry. 

Pines is a member of the Department of Chemistry.



Chemical structure of hydrated protons in liquid water. A. Schematic of the Eigen cation  H9O4+ (left) and the Zundel cation H5O2+ (right). The arrows indicate the O-H bond coordinate r and the (O…H+…O) proton transfer coordinate. In the Eigen cation a covalent O-H bond localizes the proton whereas in the Zundel cation the proton is delocalized between two water molecules. B. Anharmonic vibrational potential (left) and double minimum potential of the Zundel cation along z (right, red). Distortions by the solvent surrounding impose.​