FOR 1789:  Intermolecular and Interatomic Coulombic Decay

• Subject Area: Physics ; Chemistry
• Term: from 2012 to 2021
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 203306641

Chemical reactions and modifications of molecular structure are driven by energy. Often, this energy exists initially in the form of electronic excitations. The relaxation of electronically excited states is therefore a key question in chemistry and molecular biology. The topic of this Research Unit is the investigation of a novel, recently discovered mechanism for the transformation of electronic energy created by excitation or ionisation with UV radiation and far beyond, or energetic particles. This relaxation process has become known as Intermolecular or Interatomic Coulombic Decay (ICD). The term designates an electronic decay process occurring in weakly bonded systems, for example in many liquids. Via ICD, electronic excitation energy is transferred into kinetic energies carried by a continuum electron and the creation of two positive ions. The conditions for the occurrence of ICD are very general; it is expected they are met in many systems and situations. The first step in ICD is the creation of a single electronic vacancy, the energy of which is located above the double ionisation threshold of the weakly bonded system as a whole. An example is the ionisation of an inner valence level in water. Although such processes have been investigated for a long time, it has been predicted only in 1997 that neighbouring water molecules could be involved in the relaxation of such a vacancy. In the Intermolecular Coulombic Decay process, this primary vacancy is filled by an electron from a less strongly bound orbital, and at the same time the energy released in this transition is transferred to a neighbouring molecule, where it leads to ejection of an electron. Putting ICD in a broader context, it bridges the gap between fundamental research on the correlated motion of electrons and nuclei and more applied research, for example, on the influence of low kinetic energy electrons in radiation chemistry. The Research Unit aims to answer key questions in connection with our understanding of ICD: (1) Which physical and chemical parameters have the strongest influence on the ICD process? (2) In which systems will ICD occur? (3) In which areas of chemistry is ICD of importance? How can it be employed as a method in chemical research? (4) Does ICD have biochemical implications, e.g., in the production of radiation damage? (5) What is the time evolution of ICD?

• DFG Programme: Research Units
• International Connection: Austria

Projects

• Angular Distribution of ICD Electrons in Rare Gas Dimers (Applicant Demekhin, Philipp )
• Coordination Funds (Applicant Dörner, Reinhard )
• Detecting Interatomic and Intermolecular Coulombic Decay in clusters by fluorescence (Applicant Knie, Andre )
• Electronic cascades in microsolvated clusters initiated by resonant absorption of X-ray radiation (Applicant Gokhberg, Kirill )
• Extending teh studies of ICD in the time domain (Applicant Jahnke, Till )
• Following the evolution of ICD in time (Applicant Frühling, Ulrike )
• ICD in liquid water and in aqueous solution (Applicant Winter, Bernd Jürgen )
• Interatomic Coulombic Decay of clusters upon electron impact (Applicant Denifl, Stephan )
• Intermolecular Coulombic Decay in Biological Systems and Open-Shell Species (Applicant Dreuw, Andreas )
• Quantum state resolved ICD (Applicant Dörner, Reinhard )
• Signature and efficiency of Intermolecular Coulombic Decay in water clusters, liquid water and ice (Applicant Hergenhahn, Uwe )

• Spokesperson: Professor Dr. Reinhard Dörner