Electron attachment to uracil, thymine and cytosine

Electron attachment (EA) to uracil (U), thymine (T) and cytosine (C) was studied in the electron energy range from about 0 to 12eV using a high resolution crossed electron/molecule beams technique. The dominant negative ions formed via EA reactions to U, T and C are (U-H)(-), (T-H)(-) and (C-H)(-). The respective partial EA cross sections could be determined yielding peak values of sigma(1.0eV) = 3 x 10(-20) m(2), sigma(1.05eV) = 1.2 x 10(-19) m(2), sigma(1.54eV) = 2.3 x 10(-20) m(2). respectively. Based on (i) a comparison of the resonance positions for the different bases and on (ii) high level ab initio calculations we can assign certain resonances to the site specific loss of hydrogen during the EA reaction. At higher electron energies, in the range between about 3 and 12eV we observe further product anions (e.g., for U the ions CN-, OCN- and C3H2NO-), however, with significantly lower cross section values.