Site- and energy-selective slow-electron production through intermolecular Coulombic decay

Intermolecular Coulombic decay driven by resonant Auger decay can be used to produce low-energy electrons selectively from chosen molecular or atomic sites and with tunable energies, with possible applications in radiation therapy. Relaxation control for targeted cancer therapy The irradiation of matter with light tends to electronically excite atoms and molecules. What happens to the resulting excitation energy depends on the nature of the relaxation pathway and the energy of the electrons and ions produced. In one such pathway, known as intermolecular Coulombic decay (ICD), excess energy is transferred to neighbouring atoms or molecules that then lose an electron and become ionized. ICD electrons have relatively low energy, prompting suggestions that they might be harnessed as a form of Auger therapy — cancer treatment that uses large numbers of genotoxic low-energy electrons to damage cancer cells. In a pair of papers [in this issue of Nature ] published online this week, Gokhberg et al . propose that ICD can be triggered upon relaxation of an initial resonant core excitation, and Trinter et al . confirm the existence of the proposed excitation experimentally. The efficiency of this relaxation cascade and the fact that it can be tuned to directly control the generation site and the energy of the electrons raise the prospect of the development of more targeted cancer radiotherapy, and possibly new spectroscopic techniques. Irradiation of matter with light tends to electronically excite atoms and molecules, with subsequent relaxation processes determining where the photon energy is ultimately deposited and electrons and ions produced. In weakly bound systems, intermolecular Coulombic decay 1 (ICD) enables very efficient relaxation of electronic excitation through transfer of the excess energy to neighbouring atoms or molecules that then lose an electron and become ionized 2 , 3 , 4 , 5 , 6 , 7 , 8 , 9 . Here we propose that the emission site and energy of the electrons released during this process can be controlled by coupling the ICD to a resonant core excitation. We illustrate this concept with ab initio many-body calculations on the argon–krypton model system, where resonant photoabsorption produces an initial or ‘parent’ excitation of the argon atom, which then triggers a resonant-Auger-ICD cascade that ends with the emission of a slow electron from the krypton atom. Our calculations show that the energy of the emitted electrons depends sensitively on