Dissociative Electron Attachment to Hydrogen Halides and their Deuterated Analogs

The swarm‐beam technique has been employed to study the electron‐attachment processes in HX and DX (X = halogen) molecules. Attachment cross sections as a function of electron energy ${\sigma }_c\mathrm{(\epsilon )}$ , corrected for the finite width of the electron beam, are reported for the direct dissociative attachment, i.e., HX(or DX) + e→H (or D) + X⁻. There is a strong increase in ${\sigma }_c\mathrm{(\epsilon )}$ in going from HCl to HBr to HI, i.e., with decreasing energy of the dissociative‐attachment peak. The ratio of ${\sigma }_c\mathrm{(\epsilon )}$ for isotopic species is found to be very nearly equal to the square root of the inverse ratio of the reduced masses of the products. In addition to the direct dissociative electron attachment to HX and DX molecules, a separate attachment process occurs at thermal electron energies.