Interatomic coulombic decay (ICD)

Has been experimentally confirmed. In 1997, this new mode of atomic decay was predicted for weakly bound atoms (as in a cluster or a fluid): One atom of the cluster is excited; but a different, neighboring atom ejects a low-energy electron. A research team in Germany has now unambiguously demonstrated ICD in the smallest possible cluster of neon atoms—a dimer—with the two atoms joined by the weak van der Waals force. The removal of a tightly bound electron from one of the atoms allowed a less tightly bound electron to jump into the vacancy and thereby gain energy. The extra energy was insufficient to liberate any of the remaining electrons in that same atom, but it was sufficient to release a low-energy electron from the neighboring atom. The scientists detected ICD’s fingerprint: the two neon ions, emitted back-to-back with equal momenta, and the ejected electron, with all kinetic energies adding up to a constant. In separate work, a group in Sweden experimentally found that ICD was slower on the surface of a large neon cluster than in the bulk. That finding was consistent with the theory and showed the exquisite sensitivity of ICD to the chemical environment—in this case, the number of atomic neighbors. Though generally masked by inelastic scattering, ICD may have a wide-ranging impact in chemistry and biology; it should occur frequently in most hydrogen-bonded systems, including liquid water. (T. Jahnke et al., Phys. Rev. Lett. 93 , 163401, 2004 http://dx.doi.org/10.1103/PhysRevLett.93.163401 ; G. Öhrwall et al., Phys. Rev. Lett. 93 , 173401, 2004 http://dx.doi.org/10.1103/PhysRevLett.93.173401 .)