Temperature dependence of electron attachment to CH2ClBr: competition between Cl− and Br− formation

Dissociative electron attachment (DEA) to CH2ClBr has been studied in a crossed electron/molecular beams experiment in the electron energy range between 0 and 2 eV and in the gas temperature range between 328 and 449 K. In this electron energy range we find the two negative fragment ions Cl− and Br− which are both formed from a prominent low energy resonant feature (≈0 eV). While the Br− ion yield (recorded at ≈0 eV) considerably increases with the temperature, that of Cl− slightly decreases resulting in an overall increase of ion formation at low electron energy. The temperature dependence is interpreted by the relative disposition of the involved potential energy surfaces. For the exothermic Br− channel an activation energy of 107 ± 10 meV for the DEA reaction is obtained. Using absolute rates from swarm data the total cross section for the DEA to CH2ClBr has been calibrated to absolute values leading to 5 × 10−21 m2 at 0.5 eV.