Note: Transient negative ions as initiators of oxygen fixation in <20 eV electron-irradiated DNA

Abstract

This note represents a significant addition to our previous manuscript [N. Mirsaleh-Kohan, A. D. Bass, P. Cloutier, S. Massey, and L. Sanche, J. Chem. Phys. 136, 235104 (2012)] where we demonstrated that enhancements in the electron stimulated desorption yields of O− and OH− from O2 exposed DNA samples were due to the reactions of O2 with electron-induced damage sites within the DNA. Here, we investigate the attachment of O2 to electron-irradiated DNA as a function of electron energy and find a local maximum for O2 attachment to DNA at ∼11.4 eV. This reaction is likely initiated by the production of transient negative ions that dissociate to form RCHx−1• radicals. This work is thus relevant to our understanding of how O2 modulates radiation induced damage in cellular DNA and upon the question of the radio-sensitization of cells during, for example, radiotherapy.