Ion Chemistry Mediated by Water Networks

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Science  15 Jan 2010:
Vol. 327, Issue 5963, pp. 280-281
DOI: 10.1126/science.1184555

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The remarkable properties of liquid water derive largely from its ability to form fluctuating networks of hydrogen bonds. However, even in the gas phase, where clusters of only a few water molecules may form, their sparse hydrogen-bonded networks may still absorb energy and stabilize reactants and products (13), stabilize intermediates as catalysts (1), or act as reaction partners. In the D region of the ionosphere (70 to 85 km above Earth), the positively charged ions that form there, such as NO+, can formally transfer charge to one water molecule and add an OH group to form a neutral species (such as HONO). The resulting protonated water networks (47) are regarded as the major positive-charge carrier in the D region, which is the lowest ionospheric layer that affects radio communications. On page 308 of this issue, Relph et al. (8) report on a combined experimental and theoretical study that tries to unravel the relation between the hydrogen-bonding arrangement of a set of water molecules around an NO+ ion and the chemical activity of this ensemble. Their results bear on a key open question: Are there particular water clusters that account for most of the reactivity?