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Kamińska, Magdalena; Zhaunerchyk, Vitali; Vigren, Erik; Danielsson, Mathias; Hamberg, Mathias; Geppert, Wolf D.; Larsson, Mats; Rosén, Stefan; Thomas, Richard; Semaniak, J.

doi:10.1103/physreva.81.062701

Cited by 19 publications

(5 citation statements)

References 61 publications

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“…CH + 5 dissociative recombination experiments have been performed at both a heavy-ion storage ring (CRYRING) and in a flowing afterglow and they present some significant discrepancies in terms of both rate coefficient and branching fractions of the products. While the former set of studies reports the dominance of CH 3 +H+H (Semaniak et al, 1998;Kamińska et al, 2010), the latter observes CH 4 + H as the major products (Adams et al, 2009;Molek et al, 2009). A possible explanation is that a two-step process via the production of a CH 4 intermediate with sufficient energy to fragment further to CH 3 + H plays an important role.…”

Section: Hydrocarbon Ionsmentioning

confidence: 99%

“…The disagreement could therefore be due to a different pressure in these two experimental set-ups (< 10 −11 mbar in CRYRING versus ∼1 mbar in the flow tube). The storage ring conditions being closer to that of Titan's upper atmosphere, we prefer the values presented in Kamińska et al (2010).…”

Section: Hydrocarbon Ionsmentioning

confidence: 99%

“…(R er 104c) Geppert et al (2004b) and Vigren et al (2012a) presented results on the electron recombination of protonated cyanoacetylene: the rate coefficient at electron temperatures relevant for Titan's upper atmosphere as well as the product branching ratios. Instead of HC 3 NH + , DC 3 ND + was used for reasons concerning the detection of the fragments, but previously measured branching ratios on other small polyatomic ions (Neau et al, 2000;Jensen et al, 2000;Geppert et al, 2006;Kamińska et al, 2010) were similar for the deuterated and hydrogenated species. The channels preserving the carbon chain (D x C 3 N + (D)) or producing two fragments with a pair of heavy atoms each (C 2 D x + CND y + (D)) are detected with about equal fractions.…”

Section: Nitrogen-bearing Speciesmentioning

confidence: 99%

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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

172

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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Section: Hydrocarbon Ionsmentioning

confidence: 99%

Section: Hydrocarbon Ionsmentioning

confidence: 99%

Section: Nitrogen-bearing Speciesmentioning

confidence: 99%

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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

172

362

View full text Add to dashboard Cite

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“…125 This puzzling question has been settled based on a series of measurements of the vibrational spectrum not only of CH 5 + itself but of all its isotopologues. 88,96,[132][133][134] Much in parallel with experimental efforts the structures and energies, 4,92,110,130,131, chemical bonding and reactions, 84,93,110,111,130,135,137,149,154,160,[165][166][167][168][169][170][171][172][173][174][175] (ro-)vibrational states and transitions, 131,147,151,155,157,162,163,[176][177][178][179][180][181][182][183] as well as dynamics 129…”

Section: F Computational Aspectsmentioning

confidence: 99%

Theoretical spectroscopy using molecular dynamics: theory and application to CH5+ and its isotopologues

Ivanov

Witt

Marx

2013

Phys. Chem. Chem. Phys.

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Infrared spectroscopy is a powerful technique to unravel the structure and dynamics of molecular systems of ever increasing complexity. For isolated molecules in the gas phase theoretical approaches that directly rely on solving the Schrödinger equation, either approximately or quasi-exactly, are well established. A distinctly different approach to compute infrared spectra can be based on advanced molecular dynamics, itself being based on classical Newtonian dynamics, in conjunction with concurrent first principles electronic structure calculations. At variance with traditional methods, which are formulated in terms of the Schrödinger representation of quantum mechanics, the molecular dynamics approach stems from Heisenberg's representation and thus relies on computing thermal expectation values of time-correlation functions. Crucial in addition to generating the spectra themselves is their decomposition in terms of modes, which can be assigned to correlated atomic motion. This ab initio molecular dynamics route to compute infrared spectra, and its recent extension to quasiclassical techniques relying on approximate path integral dynamics, is covered in the review part of this Perspective. The usefulness of this unconventional approach, which can be generalized beyond infrared spectroscopy, is demonstrated in detail by applying the full machinery in computing and assigning the infrared spectra of protonated methane and its isotopologues. This particular molecule is often considered to be the most prominent member of the class of floppy or fluxional molecules. CH5(+) has been a longstanding challenge for theoretical infrared spectroscopy because it undergoes intricate large-amplitude motion, which is also reviewed. Molecular dynamics based infrared spectroscopy is general and can be applied to diverse systems such as molecular complexes in the gas phase, chromophores in biomolecular environments, and solute-solvent systems in the liquid phase.

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“…But reaction (6) is only a minor pathway in the dissociative recombination of CH5 + (branching fraction 0.05) (Semaniak et al, 1998;Kaminska et al, 2010). In spite of the apparent inefficiency of reactions (4) and (6), time-dependent models of gas-phase chemistry in a molecular cloud can make CH4 as abundant as 10 -6 (relative to H2) at a few 10 5 yr and 10 -8 at 10 8 yr (Millar et al, 1997;Woodall et al, 2007;Aikawa, 2013).…”

Section: The Fate Of Methane From Interstellar Medium To the Protosolmentioning

confidence: 99%

Methane Clathrates in the Solar System

et al. 2015

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ABSTRACT.We review the reservoirs of methane clathrates that may exist in the different bodies of the Solar System. Methane was formed in the interstellar medium prior to having been embedded in the protosolar nebula gas phase. This molecule was subsequently trapped in clathrates that formed from crystalline water ice during the cooling of the disk and incorporated in this form in the building blocks of comets, icy bodies, and giant planets. Methane clathrates may play an important role in the evolution of planetary atmospheres. On Earth, the production of methane in clathrates is essentially biological, and these compounds are mostly found in permafrost regions or in the sediments of continental shelves. On Mars, methane would more likely derive from hydrothermal reactions with olivine-rich material. If they do exist, martian methane clathrates would be stable only at depth in the cryosphere and sporadically release some methane into the atmosphere via mechanisms that remain to be determined. In the case of Titan, most of its methane probably originates from the protosolar nebula, where it would have been trapped in the clathrates agglomerated by the satellite's building blocks.Methane clathrates are still believed to play an important role in the present state of Titan.Their presence is invoked in the satellite's subsurface as a means of replenishing its atmosphere with methane via outgassing episodes. The internal oceans of Enceladus and Europa also provide appropriate thermodynamic conditions that allow formation of methane clathrates. In turn, these clathrates might influence the composition of these liquid reservoirs. Finally, comets and Kuiper Belt Objects might have formed from the agglomeration of clathrates and pure ices in the nebula. The methane observed in comets would then result from the destabilization of clathrate layers in the nuclei concurrent with their approach to perihelion.Thermodynamic equilibrium calculations show that methane-rich clathrate layers may exist on Pluto as well.

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Dissociative recombination of CH5+and CD5+:

Cited by 19 publications

References 61 publications

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

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

Theoretical spectroscopy using molecular dynamics: theory and application to CH5+ and its isotopologues

Methane Clathrates in the Solar System

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