Water jump reorientation and ultrafast vibrational spectroscopy

The reorganization of waterʹs hydrogen-bond (HB) network by breaking and making HBs lies at the heart of many of the pure liquidʹs special features and many aqueous media phenomena, including chemical reactions, ion transport and protein activity. An essential role in this reorganization is played by water molecule reorientation, long described by very small angular displacement Debye rotational diffusion. A markedly contrasting picture has been recently proposed, based on simulation and analytic modeling: a sudden, large amplitude jump mechanism, in which the reorienting water molecule rapidly exchanges HB partners in an activated process which has all the hallmarks of a chemical reaction. In this contribution, we offer a brief review of the jump mechanism together with a discussion of its application to, and probing by, modern ultrafast infrared spectroscopy experiments. Special emphasis is given to the direct characterization of the jumps via pioneering two-dimensional infrared spectroscopic measurements.