Predissociation dynamics of negative-ion resonances of H2 near 12 and 14.5 eV using the velocity slice imaging technique

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Dissociative electron attachment is an important tool for investigating negative-ion resonances. We have studied the negative-ion resonances of ${\mathrm{H}}_{2}$ at 10 and 14 eV using the improved velocity slice imaging technique. We obtained modulations in the kinetic energy spectrum of ${\mathrm{H}}^{\ensuremath{-}}$ ions obtained at 12 and 14.5 eV electron energy, consistent with the earlier reported vibrational state contributions from the higher-lying bound resonances. We show that structures obtained at 12 eV are due to predissociation of the $C{\phantom{\rule{0.16em}{0ex}}}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+}$ resonance consistent with the current understanding. However, based on our angular distribution measurements, we propose that the structures obtained at 14.5 eV are due to a predissociation of bound resonance of ${}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+}$ symmetry as against ${\mathrm{\ensuremath{\Delta}}}_{g}$ that was proposed earlier. We also report that the bound ${}^{2}{\mathrm{\ensuremath{\Sigma}}}_{g}^{+}$ resonance contributes to the observed inversion symmetry breaking near 14 eV.