Ion-momentum imaging of dissociative-electron-attachment dynamics in acetylene

Abstract

We present experimental results for dissociative electron attachment to acetylene near the 3 eV 2 Π g resonance. In particular, we use an ion-momentum imaging technique to investigate the dissociation channel leading to C 2 H − fragments. From our measured ion-momentum results we extract fragment kinetic energy and angular distributions. We directly observe a significant dissociation bending dynamic associated with the formation of the transitory negative ion. In modeling this bending dynamic with ab initio electronic structure and fixed-nuclei scattering calculations we obtain good agreement with the experiment.

Dynamics of dissociative electron attachment to ammonia

“…This is to be expected, since our structure calculations show that there is a significant energy barrier to direct dissociation. When axial recoil breaks down, we can still use the computed entrance amplitudes to predict angular distributions when we have theoretical evidence that points to how the recoil axis rotates following electron attachment, as we have shown in several previous studies [2,4,6]. Our structure calculations show that by holding H-N-H fixed and rotating the third N-H in the direction away from H-N-H, the energy at the top of the barrier drops, becoming equal to the initial resonance energy at ∼25 degrees rotation.…”

“…The dynamics associated with these dissociative processes can be complex, involving conical intersections between different anion states and multiple fragment ion product channels [1][2][3][4]. The laboratory frame angular distributions of fragment ions can provide a unique insight into understanding the breakup process since they often contain signatures of the symmetry of the resonance state and are a key ingredient in unraveling the underlying dynamics of DEA [4][5][6]. In favorable cases where the dissociation is prompt, we have shown that the theoretically obtained electron entrance amplitude, which ties the molecular-to the laboratory-frame, can be used to predict laboratoryframe angular distributions and identify specific dissociation mechanisms.…”

Distant Symmetry Control in Electron-Induced Bond Cleavage

“…The efficiency of the bond-cleavage drops with the increasing distance (alkyl chains length) between the π* system and the dissociating bond . It also leads to puzzling temperature effects and angular distributions. , The effect demonstrated here, coupling induced by motion of a distant molecular part, has been suggested, ,, but this is its first experimental evidence. However, all the prior works assumed that π* states couple to repulsive shape resonances.…”

Signatures of bond formation and bond scission dynamics in dissociative electron attachment to methane

“…[2][3][4][5] In the favorable case of prompt dissociation, characterized by the existence of predominant dissociation pathways, electronmolecule scattering calculations can tie the observed angular distributions to specific dissociation mechanisms, as shown recently in DEA to methanol 6 and acetylene. 7 Methane is a candidate of considerable interest for a detailed investigation of DEA, not only for its importance in planetary atmospheres and technological plasmas, but also because its dissociation mechanisms remain something of a mystery. The recent experimental study of Ram and Krishnakumar 8 revealed a high-level of complexity in the DEA mechanism of methane.…”