Abstract
We report experimental results on three-dimensional momentum imaging measurements of anions generated via dissociative electron attachment to gaseous formamide. From the momentum images, we analyze the angular and kinetic energy distributions for NH$_2^{-}$, O$^{-}$, and H$^{-}$ fragments and discuss the possible electron attachment and dissociation mechanisms for multiple resonances for two ranges of incident electron energies, from 5.3~eV to 6.8~eV, and from 10.0~eV to 11.5~eV. {\it Ab initio} theoretical results for the angular distributions of the NH$_2^{-}$ anion for $\sim$6~eV incident electrons, when compared with the experimental results, strongly suggest that one of the two resonances producing this fragment is a $^2$A$''$ Feshbach resonance.
Highlights
The electron-molecule collision process in which a molecule captures a low-energy electron, forms a short-lived, unstable molecular anion, and thereafter dissociates into several fragments is a long-studied process known as dissociative electron attachment (DEA)
Anions produced by DEA were accelerated towards a time-sensitive 80-mm multichannel plate (MCP) detector equipped with a position-sensitive delay-line anode
We have found that state-averaged multiconfiguration self-consistent-field (MCSCF) orbitals based on the excited neutral states, which are parents of the resonance anion states, form a good basis for characterizing the resonances as well as the excited target states
Summary
The electron-molecule collision process in which a molecule captures a low-energy electron (i.e., with energy up to ∼20 eV), forms a short-lived, unstable molecular anion, and thereafter dissociates into several fragments (one negative ion and all others neutral) is a long-studied process known as dissociative electron attachment (DEA). Studies of the dissociation pathways of formamide irradiated by (vacuum) ultraviolet light [24,25] or higher-energy radiation [26,27,28] have revealed chemical products of biological and technological relevance. Several of these reactions are expected to involve dissociative attachment by low-energy secondary electrons. We investigate whether the angular dissociation distributions and fragment kinetic-energy distributions of NH2− exhibit disparities in the 5–7-eV incident electron energy range that may allow a more direct identification of the resonances responsible for DEA. V contains concluding remarks regarding our results and future directions
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