PerspectiveUltrafast Dynamics

Charge transfer goes the distance

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Science  18 Jul 2014:
Vol. 345, Issue 6194, pp. 267-268
DOI: 10.1126/science.1255943

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The strong covalent and ionic bonds that hold molecules together form through the sharing or transfer of electrons among the constituent atoms. The dynamics of the making and breaking of chemical bonds on the natural time scale of molecular vibrations (femtoseconds) can be followed by exciting the valence electrons in molecules with ultrafast pulses from lasers operating in the near-infrared, visible, and near-ultraviolet (13). However, valence electrons tend to be delocalized within molecules, so it is difficult to obtain site-specific information about bonding in this way. Ultrafast extreme ultraviolet and x-ray sources (4, 5), as well as complementary ultrafast sources of electrons, now provide access to the more localized inner-shell electrons of selected atoms (68). As reported on page 288 of this issue, Erk et al. (9) have determined the distance at which electron or charge transfer between the fragments of a dissociating molecule becomes negligible by using a combination of ultrafast x-ray pulses, an ultrafast near-infrared laser, and a high-resolution ion-imaging spectrometer.