A dissociative electron attachment, electron transmission, and electron energy-loss study of the temporary negative ion of acetylene

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Abstract
The three title electron-impact techniques are used to study the ground and excited states of acetylene negative ion and their decay processes. The π* resonance at 2.6 eV predissociates into C2H− and H. Four narrow resonances are observed in the transmission spectrum in the 7.5–9.5 eV region and assigned to Feshbach and core-excited shape resonances with double occupation of Rydberg orbitals and ground state positive ion core. These four resonances decay into low-lying Rydberg states of neutral acetylene, the first two undergo quasiresonant autodetachment ejecting low energy (<0.7 eV) electrons, and the lowest also dissociates to yield C−2. One additional resonance is observed in the C−2 yield, which is not observable in other decay channels. The shapes of the dissociative attachment bands differ qualitatively from the band shapes of the parent and grandparent states, indicating either a strong v dependence of the dissociation rate or the admixture of σ* orbitals in some of the dissociating anion states.