Electron attachment to gas-phase uracil

We present results about dissociative electron attachment (DEA) to gas-phase uracil (U) for incident electron energies between 0 and 14 eV using a crossed electron/molecule beam apparatus. The most abundant negative ion formed via DEA is (U-H)(-), where the resonance with the highest intensity appears at 1.01 eV. The anion yield of (U-H)(-) shows a number of peaks, which can be explained in part as being due to the formation of different (U-H)(-) isomers. Our results are compared with high level ab initio calculations using the G2MP2 method. There was no measurable amount of a parent ion U(-). We also report the occurrence of 12 other fragments produced by dissociative electron attachment to uracil but with lower cross sections than (U-H)(-). In addition we observed a parasitic contaminating process for conditions where uracil was introduced simultaneously with calibrant gases SF(6) and CCl(4) that leads to a sharp peak in the (U-H)(-) cross section close to 0 eV. For (U-H)(-) and all other fragments we determined rough measures for the absolute partial cross section yielding in the case of (U-H)(-) a peak value of sigma (at 1.01 eV)=3x10(-20) m(2). (C) 2004 American Institute of Physics.