Dissociative electron attachment to DNA basic constituents: The phosphate group

Electron-stimulated desorption of H−, O− and OH− from thin films of sodium dihydrogenphosphate has been investigated in the range 0–19 eV. The yield functions exhibit a single broad peak with maxima at 8.8 ± 0.3 eV, 8.0 ± 0.3 eV, and 7.3 ± 0.3 eV, respectively, and a continuous rise above 15 eV. The structure is attributed to dissociative electron attachment causing scission of the O–H, PO and P–O bonds, which is accompanied by the corresponding formation of the stable anions H−, O− and OH−. From measurements of the time dependence of the anion signals, the effective cross-sections to damage the film near each peak energy are found to be 1.9, 1.7 and 0.9 × 10−15 cm2, respectively. The present results confirm previous conclusions on DNA damage induced by low energy electrons.