Theory and modeling of ion–molecule radiative association kinetics

Klippenstein, Stephen J.; Yang, Yong; Ryzhov, Victor; Dunbar, Robert C.

doi:10.1063/1.471201

Cited by 71 publications

(113 citation statements)

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“…Another possibility might be radiative stabilization of the C 6 H 6 intermediate(s) via emission of an infrared photon. Radiative association is known to be a plausible channel for some ionmolecule reactions (38) and hence a similar process might, in principle, produce benzene. To be efficient, the rate of radiative stabilization of the energized benzene intermediate has to be faster than that for its dissociation.…”

Section: Discussionmentioning

confidence: 99%

Formation of benzene in the interstellar medium

Jones

Zhang

Kaiser

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

143

182

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Polycyclic aromatic hydrocarbons and related species have been suggested to play a key role in the astrochemical evolution of the interstellar medium, but the formation mechanism of even their simplest building block—the aromatic benzene molecule—has remained elusive for decades. Here we demonstrate in crossed molecular beam experiments combined with electronic structure and statistical calculations that benzene (C 6 H 6 ) can be synthesized via the barrierless, exoergic reaction of the ethynyl radical and 1,3-butadiene, C 2 H + H 2 CCHCHCH 2 → C 6 H 6 + H, under single collision conditions. This reaction portrays the simplest representative of a reaction class in which aromatic molecules with a benzene core can be formed from acyclic precursors via barrierless reactions of ethynyl radicals with substituted 1,3-butadiene molecules. Unique gas-grain astrochemical models imply that this low-temperature route controls the synthesis of the very first aromatic ring from acyclic precursors in cold molecular clouds, such as in the Taurus Molecular Cloud. Rapid, subsequent barrierless reactions of benzene with ethynyl radicals can lead to naphthalene-like structures thus effectively propagating the ethynyl-radical mediated formation of aromatic molecules in the interstellar medium.

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Section: Discussionmentioning

confidence: 99%

Formation of benzene in the interstellar medium

Jones

Zhang

Kaiser

et al. 2010

Proc. Natl. Acad. Sci. U.S.A.

143

182

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“…The other, and more accurate, approach to data analysis makes use of kinetic modeling by Variational Transition State Theory (VTST) [17,18]. The input required for this model includes vibrational frequencies and infrared emission intensities that are either calculated ab initio or experimentally measured.…”

Section: Discussionmentioning

confidence: 99%

“…The stabilization of AB ϩ* occurs either through a collision with a third body (k c ␤) or through emission of photon (k r ). Radiative association experiments like the present ones use a pressure low enough for the k c process to be negligible, and analyze the competition between the k b and k r processes to yield a value for the binding energy of AB ϩ [16,17]. Two levels of sophistication were employed in the analysis of kinetic data to obtain binding energies from radiative association rate constants.…”

Section: Discussionmentioning

confidence: 99%

Reactivity and binding energies of transition metal halide ions with benzene

Gapeev

Dunbar

2002

J. Am. Soc. Mass Spectrom.

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We have generated novel halogen-ligated transition metal ions MX n ϩ (M ϭ Sc, Ti, V, and Fe, X ϭ Cl, Br and I, n ϭ 1 Ϫ 3). We have explored their reactions with benzene, a typical aromatic hydrocarbon. Attachment of one benzene molecule is usually rapid, whereas attachment of a second benzene molecule is generally much slower. The kinetics were analyzed to estimate binding energies, modeling the attachment reaction as a radiative association process. In all cases the Standard Hydrocarbon semiquantitative estimation approach was employed, and in some cases the more accurate variational transition state (VTST) kinetic modeling approach was also applied. Density functional (DFT) quantum calculations were also performed to give computed binding energies for some of the complexes. Taking previously determined binding energies for halogen-ligated alkaline-earth ions as benchmarks, it is concluded that binding of the first benzene molecule to the transition-metal species is strongly enhanced by specific chemical interactions, while binding of the second benzene molecule is more nearly electrostatic. The binding energies are not strongly dependent on the identity of the transition metal ion, and the metal-ion dependences can be rationalized in terms of valence-orbital occupations of the metals. The binding energies are nearly independent of the identity of the halogen ligands. . Cation-pi interactions in biological systems involve metal ions in their stable oxidation state (ϩ1 for alkali metals, ϩ2 for alkaline-earth metals, usually ϩ2 and ϩ3 for the transition metals). This means that gas-phase studies of singly charged systems have direct biological relevance for the alkali ions, but have less clear relevance for most other metal ions. However, using double or triply charged gas-phase metal ions in the absence of solvent leveling introduces large electrostatic interactions that are likely to swamp the chemical interactions one would like to study in the gas phase. A way to resolve this dilemma is to attach ligands to the singly charged metal, thereby raising its oxidation state to its biologically relevant value. Halogen ligands seem to be the best choice because they do not migrate from the metal center nor do they promote ion-molecule reactions.Our previous work in pursuit of this strategy [2] investigated the reactions and binding energies of singly charged, halogenated alkaline-earth metal ions with benzene and mesitylene. The binding energies of the halogen-metal ions to benzene were greatly enhanced relative to the bare metal ions, although still much smaller than the predicted binding energies of bare doubly charged ions. It appeared that the binding in these cases was well described as electrostatic in nature, and that the MX ϩ ions showed behavior intermediate between singly-charged and doubly-charged character. A useful description was that the halogenated metal ions behaved toward the benzene ligand with an effective charge between ϩ1 and ϩ2. For MgCl ϩ a simple classical-electrostatic analysis suggested an...

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“…Otherwise the complex will revert back to the initial parent species. The reaction can be decomposed into elementary steps (Klippenstein et al 1996). The first elementary step is the formation of the complex A+B → (AB + ) * with rate k f .…”

Section: Formation Of Bondsmentioning

confidence: 99%

“…The radiative rate k r can be written within the harmonic approximation as (Klippenstein et al 1996)…”

Section: Radiative Associationmentioning

confidence: 99%

Disk Chemistry

Thi

2015

EPJ Web of Conferences

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Abstract. The chemical species in protoplanetary disks react with each other. The chemical species control part of the thermal balance in those disks. How the chemistry proceeds in the varied conditions encountered in disks relies on detailed microscopic understanding of the reactions through experiments or theoretical studies. This chapter strives to summarize and explain in simple terms the different types of chemical reactions that can lead to complex species. The first part of the chapter deals with gas-phase chemistry and the second part introduces chemical reactions occurring on grain surfaces. Several terms pertaining to astrochemistry are introduced. The role of chemistry in disk and planet-formation processesChemistry are not only processes that trace the physical conditions in disks but they also plays important roles in controlling the dynamics of disks or aspects of planet formation and provide the primordial composition of planets.The most promising explanation to drive mass accretion in disks and explain the disk evolution is turbulence driven by magneto-rotational instability because molecular viscosity is inefficient on large scales. Magneto-rotational instability is a ideal-MHD phenomenon that occurs only if the gas is sufficiently ionized to couple dynamically to the magnetic fields. The strength of gas turbulence is characterized by the factor α so that the large scale turbulence can be written as ν = αc s h (with c s the sound speed and h the gas scale height of the disk). Many non-ideal MHD resistivities can restrict the development of MRI turbulence. The resistivities (Ohmic and Ambipolar diffusion) depend on the abundances of the charge carriers among other factors. Therefore the detailed knowledge of the disk ionization state is central to understand disk dynamical evolution.In planet formation, chemistry defines the disk region where water can be frozen onto grains, the so-called ice zone where grains can coagulate more easily. The ice zone is paramount to permit the formation of giant planets via the core-accretion model. The unusual C/O abundance ratios seen in exoplanets raise the question of chemical filtering in disks (Helling et al. 2014;Öberg et al. 2011). The path to complexityChemistry is also central to questions related to the origin of life. One major question is whether complex organic molecules (COMs) were originally produced in the young Earth and/or had an extraterrestrial origin. The original composition of Earth's atmosphere (and of terrestrial extrasolar planets)

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Theory and modeling of ion–molecule radiative association kinetics

Cited by 71 publications

References 50 publications

Formation of benzene in the interstellar medium

Formation of benzene in the interstellar medium

Reactivity and binding energies of transition metal halide ions with benzene

Disk Chemistry

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