The present experiments concern electron interactions with a film of short single strands of DNA covered by 3 monolayers of water, which corresponds to 5.25 water molecules per nucleotide. We report on the desorption of ${\mathrm{H}}^{-}$, ${\mathrm{O}}^{-}$, $\mathrm{O}{\mathrm{H}}^{-}$ from this target induced by $3–20\mathrm{eV}$ electrons. Below $15\mathrm{eV}$, these anions emanate principally from a new type of dissociative core-excited transient anions formed via electron capture by a DNA-${\mathrm{H}}_2\mathrm{O}$ complex. A smaller portion of the ${\mathrm{H}}^{-}$ desorption signal arises from weakly bonded ${\mathrm{H}}_2\mathrm{O}$ molecules. The overall anion yield from DNA is increased by a factor of 1.6 owing to the presence of water.

• Received 29 September 2006

DOI:https://doi.org/10.1103/PhysRevE.75.031915