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.