Dissociative ionization ofH2,D2, and HD using electron-impact excitation

Kinetic-energy distributions of ion fragments from electron-impact bombardment of ${\mathrm{H}}_2$, ${\mathrm{D}}_2$, and HD have been measured at electron energies between 30 and 100 eV. In the case of ${\mathrm{H}}_2$ these distributions at 90° are interpreted as resulting from excitation of two autoionizing states of ${\mathrm{H}}_2$ (${}_{}{}^1{}_{}{}^{}\Sigma _g^{+}{}_{}{}^{}$ and ${}_{}{}^1{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$) and one repulsive state of ${\mathrm{H}}_2^{+}\left({}_{}{}^2{}_{}{}^{}\Pi _u^{}{}_{}{}^{}\right)$. The shapes of the kinetic-energy distributions for ${\mathrm{H}}^{+}$ from ${\mathrm{H}}_2$ and ${\mathrm{D}}^{+}$ from ${\mathrm{D}}_2$ are substantially different, and a strong preference for ${\mathrm{H}}^{+}$ over ${\mathrm{D}}^{+}$ fragments from HD was observed.