Kinetics and Branching for the Reactions of N<sub>2</sub><sup>+</sup> with C<sub>3</sub>H<sub>4 </sub>Isomers at Low Temperatures and Implications for Titan’s Atmosphere - Archive ouverte HAL Accéder directement au contenu
Article Dans Une Revue ACS Earth and Space Chemistry Année : 2022

Kinetics and Branching for the Reactions of N2+ with C3H4 Isomers at Low Temperatures and Implications for Titan’s Atmosphere

Ahmad Mortada
Sophie Carles
S. Demes
Baptiste Joalland
François Lique
Abdessamad Benidar
Panayotis Lavvas

Résumé

The photoionization of N2 plays a key role in initiating the formation of complex organic molecules in the nitrogen-rich atmosphere of Saturn’s largest moon, Titan. To date, only a handful of laboratory studies have explored the reactivity of N2+ ions with hydrocarbons─limited to methane, acetylene, and ethylene─at the low temperatures relevant to Titan. Here, the rate coefficients, product identity, and branching ratios of the ion–molecule reactions of N2+ with C3H4 isomers, namely, propyne CH3CCH and allene CH2CCH2, were measured between 24 and 72 K in uniform supersonic flows. The rate coefficients are collisional and their temperature dependence is in remarkable agreement with capture models. The outcomes of both reactions are similar: they proceed primarily via dissociative charge transfer, leading to the formation of C3H3+ (main product, >70%) and C3H2+ (between 9 and 17%), whereas a second, nondissociative charge-transfer mechanism leading to C3H4+ becomes slightly more prominent as the temperature decreases (from 3 to 12%). C3H3+ is plausibly formed predominantly as the smallest aromatic cation, cyclopropenyl c-C3H3+, by following the lowest-energy pathway for the decomposition of allene and propyne cations. The measured rate coefficients and branching ratios were included in a photochemical model of Titan’s atmosphere. The results point toward a secondary role of N2+ + C3H4 reactive pathways in the production of c-C3H3+.
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hal-03634107 , version 1 (23-04-2022)

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Ahmad Mortada, Sophie Carles, S. Demes, Baptiste Joalland, François Lique, et al.. Kinetics and Branching for the Reactions of N2+ with C3H4 Isomers at Low Temperatures and Implications for Titan’s Atmosphere. ACS Earth and Space Chemistry, 2022, 6 (5), pp.1227-1238. ⟨10.1021/acsearthspacechem.1c00347⟩. ⟨hal-03634107⟩
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