Experimental studies of the dissociative recombination processes for the C6D6+and C6D7+ions

Hamberg, Mathias; Vigren, Erik; Thomas, Richard; Zhaunerchyk, Vitali; Zhang, M.; Trippel, Sebastian; Kamińska, Magdalena; Kashperka, Iryna; Ugglas, M. af; Källberg, A.; Simonsson, Ansgar; Paál, A.; Semaniak, J.; Larsson, Mats; Geppert, Wolf D.

doi:10.1051/eas/1146026

Cited by 5 publications

(6 citation statements)

References 20 publications

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“…As already shown in previous studies, the present investigation supports that the production of benzene in the upper atmospheric layers of Titan is thought to be a combination of neutral reactions and dissociative recombination of heavy aromatic ions. ,, The formation of heavy ions is described as mainly initiated by the reaction chain starting from C 2 H 5 + , which forms C 4 H 5 + by reaction with acetylene . C 4 H 5 + thereafter reacts with small hydrocarbons to form heavy ions like C 6 H 6 + and C 6 H 7 + : …”

Section: Discussionsupporting

confidence: 89%

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Aromatic Formation Promoted by Ion-Driven Radical Pathways in EUV Photochemical Experiments Simulating Titan’s Atmospheric Chemistry

et al. 2021

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In the atmosphere of Titan, Saturn's main satellite, molecular growth is initiated by 85.6 nm-Extreme UltraViolet (EUV) photons triggering a chemistry with charged and free-radical species. However, the respective contribution of these species to the complexification of matter is far from being known. This work presents a chemical analysis in order to contribute to a better understanding of aromatic formation pathways. A gas mixture N 2 /CH 4 (90/10 %) within the closed SURFACAT reactor was irradiated at relatively low pressure (0.1 mbar) and room temperature for six hours by EUV photons (∼ 85.6 nm). The neutral molecules formed at the end of the irradiation were condensed in a cryogenic trap and analyzed by electron ionization mass spectrometry. An analysis of the dominant chemical pathways highlights the identification of benzene and toluene and underlies the importance of small ion and radical reactions. On the basis of the experimental results, a speculative mechanism based on sequential Helimination/CH 3 -addition reactions is proposed for the growth of aromatics in Titan's atmosphere. Elementary reactions to be studied are given to instill future updates of photochemical models of Titan's atmosphere.

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Section: Discussionsupporting

confidence: 89%

“…As already shown in previous studies, the present investigation support that the production of benzene in the upper atmospheric layers of Titan is thought to be a combination of neutral reactions and dissociative recombination of heavy aromatic ions 16, 26,37 :…”

Section: Ion-driven Radical Chemistry Toward Benzenesupporting

confidence: 91%

Aromatic Formation Promoted by Ion-Driven Radical Pathways in EUV Photochemical Experiments Simulating Titan’s Atmospheric Chemistry

et al. 2021

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“…As highlighted in past studies Vuitton et al, 2008), electron recombination of C 6 H + 7 (R er 64) controls benzene production in the upper atmosphere. We note that the assumption that benzene is the sole product of the electron recombination of C 6 H + 7 has now been validated experimentally (Hamberg et al, 2011).…”

Section: A3a)mentioning

confidence: 84%

“…It is lost through dissociative electron recombination (R er 64), whose rate coefficient, including its evolution with electron temperature, has been recently determined (Hamberg et al, 2011). At the exception of reaction (R cn 424a), this is the same set of reactions as in Vuitton et al (2008).…”

Section: Hydrocarbon Ionsmentioning

confidence: 99%

Simulating the density of organic species in the atmosphere of Titan with a coupled ion-neutral photochemical model

Vuitton

Yelle

Klippenstein

et al. 2019

Icarus

165

362

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We present a one-dimensional coupled ion-neutral photochemical kinetics and diffusion model to study the atmospheric composition of Titan in light of new theoretical kinetics calculations and scientific findings from the Cassini-Huygens mission. The model extends from the surface to the exobase. The atmospheric background, boundary conditions, vertical transport and aerosol opacity are all constrained by the Cassini-Huygens observations. The chemical network includes reactions between hydrocarbons, nitrogen and oxygen bearing species. It takes into account neutrals and both positive and negative ions with masses extending up to about 100 u. We incorporate high-resolution isotopic photoabsorption and photodissociation cross sections for N 2 as well as new photodissociation branching ratios for CH 4 and C 2 H 2 . Ab initio transition state theory calculations are performed in order to estimate the rate coefficients and products for critical reactions.Main reactions of production and loss for neutrals and ions are quantitatively assessed and thoroughly discussed. The vertical distributions of neutrals and ions predicted by the model generally reproduce observational data, suggesting that for the small species most chemical processes in Titan's atmosphere and ionosphere are adequately described and understood; some differences are highlighted. Notable remaining issues include (i) the total positive ion density (essentially HCNH + ) in the upper ionosphere, (ii) the low mass negative ion densities (CN -, C 3 N -/C 4 H -) in the upper atmosphere, and (iii) the minor oxygen-bearing species (CO 2 , H 2 O) density in the stratosphere. Pathways towards complex molecules and the impact of aerosols (UV shielding, atomic and molecular hydrogen budget, nitriles heterogeneous chemistry and condensation) are evaluated in the model, along with lifetimes and solar cycle variations.

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“…x are thought to produce mainly benzene compounds (Hamberg et al, 2011), which are not included in this study. Moreover, since higher mass ions have lower abundances, they should have little effect on neutral chemistry up to C 4 H x .…”

Section: Positive Ion Chemistrymentioning

confidence: 99%

1D-coupled photochemical model of neutrals, cations and anions in the atmosphere of Titan

Dobrijévic

Loison

Hickson

et al. 2016

Icarus

127

169

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International audienceMany models with different characteristics have been published so far to study the chemical processes at work in Titan's atmosphere. Some models focus on neutral species in the stratosphere or ionic species in the ionosphere, but few of them couple all the species throughout the whole atmosphere. Very few of these emphasize the importance of uncertainties in the chemical scheme and study their propagation in the model.We have developed a new 1D-photochemical model of Titan's atmosphere coupling neutral species with positive and negative ions from the lower atmosphere up to the ionosphere and have compared our results with observations to have a comprehensive view of the chemical processes driving the composition of the stratosphere and ionosphere of Titan. We have updated the neutral, positive ion and negative ion chemistry and have improved the description of N2 photodissociation by introducing high resolution N2 absorption cross sections. We performed for the first time an uncertainty propagation study in a fully coupled ion-neutral model.We determine how uncertainties on rate constants on both neutral and ionic reactions influence the model results and pinpoint the key reactions responsible for this behavior. We find very good agreement between our model results and observations in both the stratosphere and in the ionosphere for most neutral compounds. Our results are also in good agreement with an average INMS mass spectrum and specific flybys in the dayside suggesting that our chemical model (for both neutral and ions) provides a good approximation of Titan's atmospheric chemistry as a whole. Our uncertainty propagation study highlights the difficulty to interpret the INMS mass spectra for masses 14, 31, 41 and we identified the key reactions responsible for these ambiguities.Despite an overall improvement in the chemical model, disagreement for some specific compounds (HC3N, C2H5CN, C2H4) highlights the role that certain physical processes could play (meridional dynamics or sticking on aerosols). We find that some critical key reactions are important for many compounds including both neutrals and ions and should be studied in priority to lower the remaining model uncertainties. Extensive studies for some specific processes (including photolyses) are required

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Experimental studies of the dissociative recombination processes for the C₆D₆⁺and C₆D₇⁺ions

Cited by 5 publications

References 20 publications

Aromatic Formation Promoted by Ion-Driven Radical Pathways in EUV Photochemical Experiments Simulating Titan’s Atmospheric Chemistry

Aromatic Formation Promoted by Ion-Driven Radical Pathways in EUV Photochemical Experiments Simulating Titan’s Atmospheric Chemistry

Simulating the density of organic species in the atmosphere of Titan with a coupled ion-neutral photochemical model

1D-coupled photochemical model of neutrals, cations and anions in the atmosphere of Titan

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