Reactions　of　O-18(2)　with　self-assembled　monolayer　films　of　thiolated　DNA　oligomers　are　studied　by　the　electron　stimulated　desorption　of　anions.　Electrons　with　energies　＜　20　eV　initiate　dehydrogenation　of　the　DNA　by　resonant　and　non-resonant　processes,　to　form　radical　sites　for　oxygenation.　This　damage　mechanism　may　underlie　the　＂oxygen　fixation＂　process　of　radiobiology.