Low energy electron stimulated desorption from DNA films dosed with oxygen

Desorption of anions stimulated by 1–18 eV electron impact on self-assembled monolayer (SAM) films of single DNA strands is measured as a function of film temperature (50–250 K). The SAMs, composed of 10 nucleotides, are dosed with O2. The OH− desorption yields increase markedly with exposure to O2 at 50 K and are further enhanced upon heating. In contrast, the desorption yields of O−, attributable to dissociative electron attachment to trapped O2 molecules decrease with heating. Irradiation of the DNA films prior to the deposition of O2 shows that this surprising increase in OH− desorption, at elevated temperatures, arises from the reaction of O2 with damaged DNA sites. These results thus appear to be a manifestation of the so-called "oxygen fixation" effect, well known in radiobiology.