Complete Branching Ratios for the Dissociative Recombination of H2O+, H3O+, and \documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \usepackage[OT2,OT1]{fontenc} \newcommand\cyr{ \renewcommand\rmdefault{wncyr} \renewcommand\sfdefault{wncyss} \renewcommand\encodingdefault{OT2} \normalfont \selectfont} \DeclareTextFontCommand{\textcyr}{\cyr} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} \landscape $\mathrm{CH}\,^{+}_{3}$ \end{document}

Dissociative recombination of the polyatomic ions H 2 O + , H 3 O + , and CH + 3 with electrons has been measured at the heavy-ion storage ring ASTRID. Complete branching ratios for all the possible product channels have been determined at zero relative energy using an energy-sensitive detector masked by grids with known transmissions. In the dissociative recombination of H 3 O + , water molecules are produced with a probability of 33%, whereas the production of atomic oxygen is negligible. Atomic carbon is, on the other hand, produced with a branching ratio of 30% in the dissociative recombination of CH + 3 . For all three molecular ions, the three-particle breakup is a major process. Relative cross sections for dissociative recombination of H 3 O + and for dissociative excitation of H 3 O + have been measured for relative electron energies up to 40 eV. Implications for the modeling of the chemistry of interstellar molecular clouds are discussed.