Multipole-moment effects in ion–molecule reactions at low temperatures: part I – ion-dipole enhancement of the rate coefficients of the He+ + NH3 and He+ + ND3 reactions at collisional energies Ecoll/kB near 0 K

<div> <div> <div> <p>A key step in gas-phase polycyclic aromatic hydrocarbon (PAH) formation involves the addition of acetylene (or other alkyne) to σ-type aromatic radicals, with successive additions yielding more complex PAHs. A similar process can happen for N- containing aromatics. In cold diffuse environments, such as the interstellar medium, rates of radical addition may be enhanced when the σ-type radical is charged. This paper investigates the gas-phase ion-molecule reactions of acetylene with nine aromatic distonic σ-type radical cations derived from pyridinium (Pyr), anilinium (Anl) and benzonitrilium (Bzn) ions. Three isomers are studied in each case (radical sites at the ortho, meta and para positions). Using a room temperature ion trap, second-order rate coefficients, product branching ratios and reaction efficiencies are reported. </p> </div> </div> </div>

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Studies of ion/molecule reactions, ion mobilities, and their temperature dependence to very low temperatures using a liquid-helium-cooled ion drift tube

International Journal of Mass Spectrometry and Ion Physics ◽

10.1016/0020-7381(83)85076-1 ◽

1983 ◽

Vol 49 (1) ◽

pp. 61-83 ◽

Cited By ~ 57

Author(s):

H. Böhringer ◽

F. Arnold

Keyword(s):

Temperature Dependence ◽

Liquid Helium ◽

Low Temperatures ◽

Drift Tube ◽

Ion Drift ◽

Ion Molecule Reactions

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Molecular-physics aspects of cold chemistry

Current Trends in Atomic Physics ◽

10.1093/oso/9780198837190.003.0003 ◽

2019 ◽

pp. 82-141

Author(s):

FrÉdÉric Merkt

Keyword(s):

Low Temperature ◽

Low Temperatures ◽

Molecular Physics ◽

Exothermic Reactions ◽

Langevin Model ◽

Ion Molecule Reactions ◽

Radiative Association ◽

Association Reaction ◽

Oppenheimer Approximation ◽

General Aspects

Molecular-physics aspects of cold chemistry are introduced with the example of few-electron molecules. After a brief overview of general aspects of molecular physics, the solution of the molecular Schrödinger equation is presented based on the Born-Oppenheimer approximation and the subsequent evaluation of adiabatic, nonadiabatic, relativistic and radiative (QED) corrections. Low-temperature chemical phenomena are introduced with the example of ion-molecule reactions, using the classical Langevin model for barrier-free exothermic reactions as reference. Then, methods to generate cold few-electron molecules by supersonic-beam-deceleration methods such as Stark, Zeeman, and Rydberg-Stark decelerations are presented. Two astrophysically important reactions, the reaction between H2 and H2+ forming H3+ and H, a very fast reaction following Langevin-capture going over to quantum-Langevin capture at low temperature, and the radiative association reaction H+ + H forming H2+, a very slow reaction in which quantum effects (shape resonances) become important at low temperatures, are used to illustrate the concepts introduced.

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The Formation of Interstellar Molecules via Radiative Association Reactions

Symposium - International Astronomical Union ◽

10.1017/s0074180900072806 ◽

1980 ◽

Vol 87 ◽

pp. 323-324

Author(s):

David Smith ◽

Nigel G. Adams

Keyword(s):

Rate Coefficients ◽

Rate Data ◽

Association Rate ◽

Interstellar Molecules ◽

Ion Molecule Reactions ◽

Radiative Association ◽

Temperature Dependences ◽

Association Reaction

The radiative association rate coefficients and their temperature dependences have been estimated for several likely interstellar ion-molecule reactions from laboratory collisional association rate data. They include the CH3+ + H2 and CH3+ + H2O reactions, which we suggest lead to CH4 and CH3OH respectively, and the critical association reaction C+ + H2.

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Kinetic Energy Dependence of Ion–Molecule Reactions Related to Plasma Chemistry

Advances In Atomic, Molecular, and Optical Physics - Fundamentals of Plasma Chemistry ◽

10.1016/s1049-250x(08)60125-1 ◽

2000 ◽

pp. 187-229 ◽

Cited By ~ 7

Author(s):

P.B. Armentrout

Keyword(s):

Kinetic Energy ◽

Energy Dependence ◽

Plasma Chemistry ◽

Ion Molecule Reactions

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Low temperature gas phase reaction rate coefficient measurements: Toward modeling of stellar winds and the interstellar medium

Proceedings of the International Astronomical Union ◽

10.1017/s1743921319007531 ◽

2019 ◽

Vol 15 (S350) ◽

pp. 382-383

Author(s):

Niclas A. West ◽

Edward Rutter ◽

Mark A. Blitz ◽

Leen Decin ◽

Dwayne E. Heard

Keyword(s):

Low Temperature ◽

Interstellar Medium ◽

Gas Phase ◽

Low Temperatures ◽

Reaction Rate ◽

Rate Coefficient ◽

Building Blocks ◽

Rate Coefficients ◽

Stellar Winds ◽

Phase Reaction

AbstractStellar winds of Asymptotic Giant Branch (AGB) stars are responsible for the production of ∼85% of the gas molecules in the interstellar medium (ISM), and yet very few of the gas phase rate coefficients under the relevant conditions (10 – 3000 K) needed to model the rate of production and loss of these molecules in stellar winds have been experimentally measured. If measured at all, the value of the rate coefficient has often only been obtained at room temperature, with extrapolation to lower and higher temperatures using the Arrhenius equation. However, non-Arrhenius behavior has been observed often in the few measured rate coefficients at low temperatures. In previous reactions studied, theoretical simulations of the formation of long-lived pre-reaction complexes and quantum mechanical tunneling through the barrier to reaction have been utilized to fit these non-Arrhenius behaviours of rate coefficients.Reaction rate coefficients that were predicted to produce the largest change in the production/loss of Complex Organic Molecules (COMs) in stellar winds at low temperatures were selected from a sensitivity analysis. Here we present measurements of rate coefficients using a pulsed Laval nozzle apparatus with the Pump Laser Photolysis - Laser Induced Fluorescence (PLP-LIF) technique. Gas flow temperatures between 30 – 134 K have been produced by the University of Leeds apparatus through the controlled expansion of N2 or Ar gas through Laval nozzles of a range of Mach numbers between 2.49 and 4.25.Reactions of interest include those of OH, CN, and CH with volatile organic species, in particular formaldehyde, a molecule which has been detected in the ISM. Kinetics measurements of these reactions at low temperatures will be presented using the decay of the radical reagent. Since formaldehyde and the formal radical (HCO) are potential building blocks of COMs in the interstellar medium, low temperature reaction rate coefficients for their production and loss can help to predict the formation pathways of COMs observed in the interstellar medium.

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Termolecular ion–molecule reactions involving C3H5+

Canadian Journal of Chemistry ◽

10.1139/v70-594 ◽

1970 ◽

Vol 48 (22) ◽

pp. 3549-3553 ◽

Cited By ~ 1

Author(s):

A. G. Harrison ◽

A. A. Herod

Keyword(s):

Kinetic Energy ◽

Molecular Size ◽

Order Rate Constant ◽

Second Order ◽

Rate Coefficients ◽

Third Order ◽

Order Rate ◽

Ion Molecule Reactions ◽

Similar Dependence ◽

Ion Kinetic Energy

The reaction of C3H5+ with C2D4 to produce C5H5D4+ is shown to be second order in C2D4. The rate coefficients are in the range 10−24 to 10−25 cm6 molecule−2 s−1 but decrease markedly with increasing ion kinetic energy. This decrease reflects the effect of the ion kinetic energy on the lifetime of the initial collision complex. Small differences in rate coefficients are observed depending on the source of the C3H5+ ion but these are insufficient to distinguish between possibly different ionic structures. The reaction of C3H5+ with C2H3F forms C5H7+ in a reaction second order in C2H3F. The rate coefficients are also in the range 10−24 to 10−25 cm6 molecule−1 s−1 and show a similar dependence on ion kinetic energy. These high third order rate constants are compared with data for other termolecular reactions and are shown to be consistent with the effect of molecular size on the third order rate constant.

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