Absolute cross sections for dissociative electron attachment to HCl, HBr, and their deuterated analogs

Abstract

We have measured absolute dissociative electron attachment cross sections for $\mathrm{H}X$ and $\mathrm{D}X$ ($X=\mathrm{Cl}$ and Br) using a trochoidal electron spectrometer equipped with a total ion collection collision chamber, operated both in a field-free passive ion collection mode, and an active ion collection mode, with an extracting electric field. Our results for ${\mathrm{Br}}^{\ensuremath{-}}$ from HBr are in an excellent quantitative agreement with recent predictions of the nonlocal resonance model, but the cross sections for ${\mathrm{Cl}}^{\ensuremath{-}}$ from HCl and DCl are, respectively, 2.2 times and 2.8 times smaller than the theoretical predictions. Cross sections for the production of ${\mathrm{H}}^{\ensuremath{-}}$ and ${\mathrm{D}}^{\ensuremath{-}}$ in the $6--10\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ range are much smaller than those for ${X}^{\ensuremath{-}}$ and the isotope effect is much weaker, consistent with the assignment to core-excited Feshbach resonances. There is one exception, however, the $9\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ band in HCl has a large isotope effect.