High energetic radiation leads to mutations and damages of biological tissue on a molecular level. It turned out that low energy electrons (E_kin < 15 eV) play an important role in this processes. To get a better understanding about the ongoing processes we also carry out experiments with biomolecules. Another important topic in this research area is related to the stability of radiosensitisers towards the irradiation with low energy electrons. These molecules are used in oncology to improve the sensitivity of tumor cells towards radiation.

Recent Highlight:

Resonant Formation of Strand Breaks in Sensitized Oligonucleotides Induced by Low-Energy Electrons (0.5-9 eV)

Robin Schürmann, Thupten Tsering, Katrin Tanzer,  Stephan Denifl, Sunil Kumar, Ilko Bald

Angew.Chem.Int.Ed. 2017, 56, 10952

DOI:10.1002/anie.201705504

In recent years, the interatomic Coulombic decay (ICD) has become known as an important relaxation process in weakly bonded systems, like for example atomic and molecular clusters and liquids. In ICD the excess energy deposited in a cluster by a collision with another particle (electron, photon, ion) is transferred by exchange of a virtual photon to a neighbouring atom, thereby ionizing it and emitting an ICD electron. In collaboration with the group of Dr. Alexander Dorn from the MPI Heidelberg we recently investigated ICD in argon dimers ionized by electron impact. The relaxation process of radiative charge transfer (RCT) may also occur in the Ar dimer in which one atom is doubly ionized, and an electron is transferred from a neighbour-atom to the doubly charged Ar²⁺ ion. The system can relax by emitting a photon. Both ICD and RCT processes result in two repulsive Ar⁺ ions and hence the separation of both processes is highly challenging in an experiment. Utilizing the reaction microscope build by A. Dorn at the MPI, we were recently able to identify both processes.

Direct evidence of two interatomic relaxation mechanisms in argon dimers ionized by electron impact

Xueguang Ren, Elias Jabbour Al Maalouf, Alexander Dorn and Stephan Denifl 

Nature Communications, 2016, 7, Article number: 11093 

doi:10.1038/ncomms11093

Complete ligand loss in electron ionization of the weakly bound organometallic tungsten hexacarbonyl dimer

Michael Neustetter, Andreas Mauracher, Paulo Limão-Vieira and Stephan Denifl 

Phys. Chem. Chem. Phys., 2016, 18, 9893-9896

The formation of negative ions upon collisions of free electrons with neutral particles is a resonant process, i.e. the reaction only occurs at specific electron energies. Utilization of a homebuilt hemispherical electron monochromator allows further study of such processes with high energy resolution (<100meV). Hence we can determine the energy dependence of the anion formation with high precision.The monochromator is coupled to a quadrupole mass spectrometer in order to detect the product ions upon inelastic electron interaction.

One interesting aspect we are currently investigating is the role of rare gas matrices on the electron attachment process. Rare gas clusters are doped with molecules and irradiated by low energy electrons. The anion yield of molecular clusters formed in the rare gas matrix elucidates then the influence of the matrix. The results are important for many different research areas like for example radiation chemistry, atmospheric chemistry, astrochemistry, material sciences, etc.

DOI:10.1021/acs.jpclett.7b00691