Observations of Diatomic and Triatomic Hydrogen Negative Ions

Mass-spectrometric observations have been made of H${\mathrm{D}}^{\ensuremath{-}}$, ${\mathrm{D}}_{2}^{\ensuremath{-}}$, ${\mathrm{H}}_{3}^{\ensuremath{-}}$, ${\mathrm{H}}_{2}$${\mathrm{D}}^{\ensuremath{-}}$, H${\mathrm{D}}_{2}^{\ensuremath{-}}$, and ${\mathrm{D}}_{3}^{\ensuremath{-}}$, using a hollow-cathode duoplasmatron negative-ion source operating between 0.1 and 2 Torr. Both the diatomic and triatomic hydrogen negative ions appear stable, with half-lives greater than ${10}^{\ensuremath{-}5}$ sec. Attenuation-cross-section measurements of ${\mathrm{D}}_{2}^{\ensuremath{-}}$ and ${\mathrm{D}}_{3}^{\ensuremath{-}}$ with helium between 3 and 5 keV yield average values of (5.5 and 7.0) \ifmmode\times\else\texttimes\fi{} ${10}^{\ensuremath{-}15}$ ${\mathrm{cm}}^{2}$, respectively.