Negative-Ion Formation inH2O andD2O

The electron swarm-beam technique was employed to determine the dissociative attachment cross sections for ${\mathrm{H}}_2$O and ${\mathrm{D}}_2$O. The formation of ${\mathrm{H}}^{-}$ from ${\mathrm{H}}_2$O peaked at an energy, ${\epsilon }_{max}$, equal to 6.5±0.1 eV, and the cross section ${\sigma }_c\left({\epsilon }_{max}\right)$ for the process at ${\epsilon }_{max}$ was found to be 6.9×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$. For ${\mathrm{D}}^{-}$ from ${\mathrm{D}}_2$O, ${\epsilon }_{max}$ was 6.5±0.1 eV and ${\sigma }_c\left({\epsilon }_{max}\right)$ was 5.2×${10}^{-18\mathrm{}}$ ${\mathrm{cm}}^2$. Data on the formation of ${\mathrm{O}}^{-}$ from ${\mathrm{H}}_2$O and ${\mathrm{D}}_2$O are also presented. Interesting isotope effects in the cross section for the formation of ${\mathrm{H}}^{-}$ from ${\mathrm{H}}_2$O and ${\mathrm{D}}^{-}$ from ${\mathrm{D}}_2$O, and the relative ion yields of the three ${\mathrm{O}}^{-}$ peaks from ${\mathrm{H}}_2$O and ${\mathrm{D}}_2$O were observed and are discussed in relation to existing theories for dissociative electron attachment. Data are also reported for ion-molecule reactions occurring in ${\mathrm{H}}_2$O and in ${\mathrm{H}}_2$O-${\mathrm{O}}_2$ mixtures.