Electron attachment to the DNA bases thymine and cytosine

Electron attachment (EA) to the DNA bases thymine (T) and cytosine (C) was studied in the electron energy range from about 0 to 9 eV using a crossed electron/molecule beams technique. As uracil the dominant negative ions formed via EA reactions to T and C are (T − H)− (corresponding to T minus H, with a mass to charge ratio of 125) and (C − H)− (corresponding to C minus H with a mass to charge ratio of 110). The respective partial EA cross-sections for (T − H)− and (C − H)− could be determined yielding peak values of σ (1.05 eV)=1.2 × 10−19 m2, σ (1.54 eV)=2.3 × 10−20 m2, respectively.