The aim of this work is to advance our understanding of how the chemical environment affects low-energy electron interactions with biomolecules, notably DNA constituents. Electron attachment processes play an important role in radiation damage to biological material. In particular, electrons released by the ionization of local molecules (mainly water) can lose energy in a series of collisions before attaching to nucleobases in DNA. The resultant negative ions may be unstable and hence fragment yielding reactive species. A high density of such dissociation events in DNA constitutes a clustered lesion, recognized as a key precursor to mutations and cancers. Detailed knowledge of how electrons attach to biomolecules in a hydrogen-bonded environment and the stabilities of the resultant anionic states is therefore essential to understand radiation damage on the molecular scale. Moreover, characterising low-energy electron interactions with clustered biomolecules can inform how dopants affect radio-sensitivity with applications in radiotherapy and radiation protection.

The research is centred on the irradiation of biomolecular isomers and clusters with electrons at precisely defined energies and analysis of the resultant anions by mass spectrometry. The experiment is currently being tested and incorporates a Stark deflector developed by Jochen Kupper and co-workers at DESY to deflect polar species in inhomogeneous electric fields in order to enhance control over the target configurations. To date, comparisons with theory have been limited by the spread of biomolecular isomers and clusters in crossed-beam experiments. The project is being carried out in collaboration with Jimena Gorfinkiel and Ilya Fabrikant, theoreticians at the OU and University of Nebraska innovating methods to simulate low-energy electron interactions with clusters.

As a complement to the Stark deflection approach, we are developing an additional system to control neutral beams for EA experiments. Stark deflection can provide target configuration specificity for relatively small molecules and complexes but is less practical for larger systems due to decreasing dipole moment / mass ratios and difficulty in producing rotationally cold beams. The new method will select only on the basis of mass but can be applied to large clusters. It involves the neutralization of mass-selected cluster anions by electron photo-detachment from weakly bound anionic states, with minimal change in stability and hence dissociation. Our aim is use the method to determine absolute electron attachment cross sections for comparisons with theoretical calculations.

From the applied perspective, we are carrying out this research in collaboration Gustavo Garcia (CSIC, Madrid) who is developing radiation track simulations that incorporate electron-attachment induced processes. The integrated research programme will help to bridge the complexity gap between understanding radiation-induced processes in isolated molecules and in condensed material, with applications in modelling and potentially modifying biological damage on the nanoscale.