Chapter 5 - Electronic Decay Cascades in Chemical Environment

Abstract

Core-excited and core-ionized states created by absorption of X-ray photons carry an enormous energy of hundreds to thousands electronvolts. In the gas phase this energy is dissipated primarily in the Auger decay process or Auger decay cascades, whereby one or several electrons are emitted into the continuum producing multiply charged ions. Two interatomic electronic decay processes, interatomic Coulombic decay (ICD) and electron-transfer mediated decay (ETMD), ensure the efficient dissipation of energy beyond the Auger decay should X-ray absorption take place in a chemical medium characterized by weak van der Waals or hydrogen bonds. Numerous experiments and theoretical results have demonstrated that the Auger–interatomic decay cascades represent a common de-excitation mechanism of core vacancies in medium, whose length and complexity increase with increasing photon energy. Such cascades offer a means for very fast dissipation of the energy which is deposited by the photon into the system. They are also responsible for massive radiation damage to the molecules around the photoabsorption site. Surprisingly, ICD cascades remain a potent mechanism of energy dissipation also when the energy is invested in a cluster by a laser not as a single high energy photon but as multiple low energy ones. The recent research of the electronic decay in chemical media presented in this chapter strives to clarify the physical and chemical consequences of weakly subjecting bound clusters to the highly energetic light provided by modern light sources.