Excited neutral triatomic hydrogen and deuterium molecules formed by electron-impact excitation have been investigated. We report on the autoionization of ${\mathrm{H}}_3^{\mathrm{*}}$ and ${\mathrm{D}}_3^{\mathrm{*}}$ molecules produced by the reactions ${\mathrm{H}}_2^{+}$+${\mathrm{H}}_2$→${\mathrm{H}}_3^{\mathrm{*}}$+${\mathrm{H}}^{+}$ and ${\mathrm{D}}_2^{+}$+${\mathrm{D}}_2$→${\mathit{D}}_3^{\mathrm{*}}$+${\mathrm{D}}^{+}$. We measured the lifetime of ${\mathrm{H}}_3^{\mathrm{*}}$ and ${\mathrm{D}}_3^{\mathrm{*}}$ and the branching ratio between ${\mathrm{H}}_3^{\mathrm{*}}$, ${\mathrm{D}}_3^{\mathrm{*}}$, and ${\mathrm{H}}_3^{+}$, ${\mathrm{D}}_3^{+}$ production channels.

• Received 9 April 1992

DOI:https://doi.org/10.1103/PhysRevA.47.986