Ionic Polymerization in Cold Plasmas of Acetylene with Ar and He

Abstract

The ionic polymerization of acetylene in cold plasmas of C 2 H 2 /He and C 2 H 2 /Ar has been experimentally studied and modeled in radio frequency (rf) discharges with conditions selected to avoid particle formation. Steady-state distributions of positive and negative ions were measured with mass spectrometry. All the measured distributions are dominated by ions with an even number of carbon atoms, reflecting the characteristic polyyne structures typical for the polymerization of acetylene. The distributions show a monotonic decrease in intensity from ions with two carbon atoms until the highest number of atoms detected. For cations, the distributions extend until 12 carbon atoms. The anion distributions extend further, and negative ions with 20 C atoms are observed in the C 2 H 2 /Ar plasma. From the measured mass spectra it is not possible to decide on the possible presence of aromatic species in ions with more than six carbon atoms. A simple model assuming a homogeneous discharge was used to describe the plasma kinetics and could account for the measured ion distributions with reasonable values of charge density and electron temperature. The results of this work stress the important role of the vinylidene anion and indicate that Ar and He do not have much influence on the carbon chemistry.

The Chemistry of Cosmic Dust Analogs from C, C2, and C2H2 in C-rich Circumstellar Envelopes

“…This is different to the case of dusty plasmas in which apart from the neutral dissociative production of C 2 H, there is a higher probability for the formation of C 2 + H 2 (from C 2 H 2 ) and C 2 H + (from C 2 H) by electron knocking-off and dissociative ionization processes, respectively. Thus, the chemistry of the formation of NPs in C 2 H 2 dusty plasmas presents a nonnegligible ion-neutral contribution (Jiménez-Redondo et al 2019). In addition, anionic polymeryzation routes can be relevant in acetylene plasmas (Deschenaux et al 1999;De Bleecker et al 2006b;Jiménez-Redondo et al 2019) due to the trapping of negative ions in the plasma potential, despite the electron attachment probability being several orders of magnitude lower than those for electron impact dissociation/ ionization.…”

“…Thus, the chemistry of the formation of NPs in C 2 H 2 dusty plasmas presents a nonnegligible ion-neutral contribution (Jiménez-Redondo et al 2019). In addition, anionic polymeryzation routes can be relevant in acetylene plasmas (Deschenaux et al 1999;De Bleecker et al 2006b;Jiménez-Redondo et al 2019) due to the trapping of negative ions in the plasma potential, despite the electron attachment probability being several orders of magnitude lower than those for electron impact dissociation/ ionization. However, the chemistry involving anions is very unlikely in SGASs, in which it has been shown that the chemistry proceeds predominantly by neutral-neutral interactions (Haberland et al 1991;Martínez et al 2020) .…”

The chemistry of cosmic dust analogues from C, C$_2$, and C$_2$H$_2$ in C-rich circumstellar envelopes

“…This is different to the case of dusty plasmas in which apart from the neutral dissociative production of C 2 H, there is a higher probability for the formation of C 2 H + 2 (from C 2 H 2 ) and C 2 H + (from C 2 H) by electron-knocking off and dissociative ionization processes, respectively. Thus, the chemistry of the formation of nanoparticles in C 2 H 2 dusty plasmas presents a non-negligible ion-neutral contribution (Jimnez-Redondo et al 2019). In addition, anionic polymeryzation routes can also be relevant in acetylene plasmas (Deschenaux et al 1999;De Bleecker et al 2006b;Jimnez-Redondo et al 2019) due to the trapping of negative ions in the plasma potential, despite the electron attachment probability being several orders of magnitude lower than those for the electron impact dissociation/ionization.…”

“…Thus, the chemistry of the formation of nanoparticles in C 2 H 2 dusty plasmas presents a non-negligible ion-neutral contribution (Jimnez-Redondo et al 2019). In addition, anionic polymeryzation routes can also be relevant in acetylene plasmas (Deschenaux et al 1999;De Bleecker et al 2006b;Jimnez-Redondo et al 2019) due to the trapping of negative ions in the plasma potential, despite the electron attachment probability being several orders of magnitude lower than those for the electron impact dissociation/ionization. However, the chemistry involving anions is very unlikely in SGAS, in which it has been shown that the chemistry proceeds predominantly by neutral-neutral interactions (Haberland et al 1991;Martínez et al 2020) .…”

Cooperativity of the Activated CH/π Interaction Probed through CH Stretching Vibrations in Phenol–(Acetylene)n(∼16 ≤n≤ ∼30) and (Acetylene)n+(10 ≤n≤ 70) Clusters

“…An alternative candidate to probe the size dependence of the activated CH/π interaction among acetylene molecules is (acetylene) n + cluster cations. − Because of the excess charge, mass spectrometric techniques are applicable to rigorously select the size of ionic clusters. Of course, the excess charge would largely enhance intermolecular interactions of surrounding molecules, and its effect cannot be ignored.…”