Dissociative electron attachment and dipolar dissociation in ethylene

Abstract

We present a detailed experimental investigation of anion production in electron collisions with ethylene, C 2 H 4 . The investigated energy range is between 0 and 90 eV where anions are formed by two processes, in the low energy regime by dissociative electron attachment (DEA) and at higher energy by dipolar dissociation (DD). These electron induced processes are studied in two different experimental apparatus using two different mass spectrometry techniques. One is a time of flight spectrometer operating with velocity slice imaging technique and the other is a two sector field mass spectrometer. The former allows efficient collection of ions compared to standard mass spectrometers, while the latter provides high mass resolution. Eight fragment anions formed via DEA in the electron energy range between 5 and 17 eV have been detected; two fragments have not reported as DEA products in any previous studies. DD in C 2 H 4 leads to the formation of the same anions as found in the case of DEA. Quantum chemical calculations have been carried out to determine the thermochemical thresholds of anion formation.

Low-energy elastic electron scattering from ethylene: Elastic scattering and vibrational excitation

“…Above 15eV, the neglect of ionization and other significant open channels makes electron-polyatomic elastic scattering models of the SMC type less accurate and gives riseto disagreement between theory and experiment. At higher E 0 , agreement of the present experiment with those of Panajotovic et al[8] and of Mapstone and Newell[5] is very good to…”

“…Low energy DEA of ethylene, giving rise to Hanions, was recently measured by Cadez et al [4] who observed a weak, composite structure of 3 overlapping features at 7.5eV, 9eV and 10.7eV. More recently, the more detailed DEA measurements of Szymańska et al [5] confirmed this Hstructure, but in addition were also able to observe C -, CH - Electronically elastic scattering coupled to vibrational excitation of ethylene has also been previously studied, focused on resonant scattering involving electron attachment to the C=C and the C-H 2 bond systems. Elastic scattering measurements were made by Mapstone and Newell [6], Panajotovic et al [8], Khakoo et al [9] and by Allan et al [1].…”

“…The dynamics of low energy electron attachment to the C=C double bond is of great interest as this gives rise to vibrational resonances. In some molecules this can cause dissociation (dissociative electron attachment, DEA), but not in ethylene, where electronic excitation is more likely to cause dissociation [1,4,5]. Ethylene is the simplest molecule that comprises the C=C bond and thus the simplest to look at resonances associated with this bond.…”

Electron-Induced Chemistry in the Condensed Phase

“…While this needs to corrected for stabilization of the ion, a shift of around 4 eV cannot be explained in this way, ruling out DEA to water as the initiating step in the reaction. DEA cross-sections to C 2 H 4 have also been reported, by Szymańska et al [24], but in much the same way as in water, no anion formation was observed below 6 eV. The only process that is known to occur is a non-dissociative electron attachment to water at around 1.5 eV.…”

Low energy electron attachment to cyanamide (NH2CN)

“…In this case we can exclude DEA from hydrocarbons present in the vacuum chamber since for these compounds resonances are only found at substantially higher electron energies. 51…”