Electron attachment to halocarbons of environmental interest: Chloroethanes

Electron attachment to the chlorofluoroethanes 1,1-C2Cl2F4, 1,2-C2Cl2F4, 1,1,1-C2Cl3F3, and 1,1,2-C2Cl3F3 was investigated in dilute mixtures with nitrogen and argon using the electron swarm method. The 1,1,1-C2Cl3F3 molecule has a very large electron attachment rate constant at thermal energy (2.8×10−7 cm3 s−1); the rate constant for this molecule decreases monotonically with increasing electron energy above thermal. The other chlorofluoroethanes investigated attach electrons less strongly and show maxima in the rate constant vs mean electron energy at ∼0.5 eV. For all four compounds, the measured rate constants are due primarily to dissociative electron attachment producing Cl−. Electron attachment cross sections were determined for these halocarbons which showed the existence of several negative ion states below ∼2 eV. Additionally, the temperature dependence of electron attachment to 1,1-C2Cl2H4 was investigated from 323–473 K. The measured rate constants and unfolded cross sections indicated electron attachment to a repulsive negative ion state from the v=0 and v=1 levels of the neutral molecule.