The Pressure Dependance of Ion-Molecule Reaction Rate Coefficients: CH3+ + HCN/He

1985 ◽  
Vol 38 (2) ◽  
pp. 231 ◽  
Author(s):  
RG Gilbert ◽  
MJ McEwan
Keyword(s):  
Reaction Rate ◽  
Rate Coefficients ◽  
Molecule Reaction ◽  
Ion Molecule Reactions ◽  
Methyl Isocyanide ◽  
Microscopic Reaction ◽  
Energy Dependent ◽  
Collisional Energy Transfer ◽  
Activated Complex ◽  
Transfer Probability

Illustrative calculations are presented on the application to termolecular ion-molecule reactions of methods recently developed for the study of fall-off effects in neutral thermal unimolecular reactions. The energy-dependent microscopic reaction rate, k(E), is obtained from RRKM theory with activated complex parameters first estimated by using ab initio and spectroscopic data and then refined to yield the appropriate pressure-saturated rate. The collisional energy transfer probability distribution function, P(E,E′), is obtained by fitting the fall-off data, guided by information from trajectory calculations. Overall rate coefficients are computed from accurate solutions to the appropriate integral master equation. The illustrative calculations are for the CH3+ + HCN+He → C2H4N+ +He system. It is shown that pressure-dependent data for ion-molecule systems can yield reliable information on P(E,E′). Collisions with the bath gas (He) are comparatively weak, with the average downward energy transferred per collision being c. 8 kJ mol-1. The product of the reaction before any isomerization can occur is shown to be protonated methyl isocyanide , H3CNCH+.

scholarly journals Ion-Molecule Reaction Studies below 80 K by the CRESU Technique

1987 ◽  
Vol 120 ◽  
pp. 19-23
Author(s):  
J. B. Marquette ◽  
B. R. Rowe ◽  
G. Dupeyrat ◽  
G. Poissant
Keyword(s):  
Low Temperatures ◽  
Reaction Rate ◽  
Thermal Conditions ◽  
Polar Molecule ◽  
Rate Coefficients ◽  
Third Body ◽  
Basic Principles ◽  
Molecule Reaction

The basic principles of the CRESU technique (Cinétique de Réactions en Ecoulement Supersonique Uniforme) are presented. This technique allows ion-molecule reaction rate coefficients under true thermal conditions at interstellar temperatures. Various behaviors of both third-body association and binary reactions with temperature have been observed, including ion-polar molecule reactions whose rate coefficients sharply increase at very low temperatures.

Unimolecular reactions of N2O and CO2 at high pressure

1979 ◽  
Vol 57 (13) ◽  
pp. 1731-1742 ◽  
Author(s):  
Andrew W. Yau ◽  
Huw O. Pritchard
Keyword(s):  
High Pressure ◽  
Spectroscopic Data ◽  
Degrees Of Freedom ◽  
Room Temperature ◽  
Reaction Rate ◽  
Probability Function ◽  
Adjustable Parameter ◽  
Rate Coefficients ◽  
Microscopic Reaction ◽  
Arrhenius Expression

An apriori calculation in the framework of the theory of radiationless transitions is presented for the non-adiabatic spin-forbidden reactions of N2O and CO2. The calculation is two-dimensional, incorporating the two stretching degrees of freedom, and the microscopic reaction process is formulated using the relative coordinate system of Rosen as modified by Beswick and Jortner. All microscopic parameters required for the calculation are derived from spectroscopic data; no adjustable parameter is included. For each reaction, a purely theoretical reaction probability function k(E) is synthesised and used to derive a theoretical Arrhenius expression for the infinite-pressure reaction rate. The calculated high-pressure unimolecular dissociation rates for both reactions are in reasonable agreement with experiment. High-pressure recombination rate coefficients are also presented for CO2; they exhibit positive activation energies which increase from 0.5 kcal/mol at room temperature to 8 kcal/mol at 5000 K.

A reformulation of the theory of unimolecular reactions

1978 ◽  
Vol 56 (10) ◽  
pp. 1389-1414 ◽  
Author(s):  
Andrew W. Yau ◽  
Huw O. Pritchard
Keyword(s):  
Energy Levels ◽  
Normal Modes ◽  
Present Theory ◽  
Vibration Energy ◽  
Unimolecular Reactions ◽  
Methyl Isocyanide ◽  
Master Equation Approach ◽  
Microscopic Reaction ◽  
Reaction Processes ◽  
Activated Complex

The theory of unimolecular reactions is reformulated in a way which makes no reference to the concepts of a transition state, a reaction coordinate, or of an activated complex: the present theory is based, instead, on a simple master-equation approach using the estimated positions and lifetimes of the rotation–vibration energy levels of the molecule. The fundamental basis of this reformulation is that the unimolecular rate is derived from the perturbation of the normal modes of internal relaxation of the reactant molecule by the microscopic reaction processes. The thermal decompositions of cyclobutane, cyclopropane, ethyl isocyanide, ethyl chloride, and methyl isocyanide are examined in detail, and it is shown that not only is the present theory much easier to use than is conventional RRKM theory, but also that it gives better results.An Appendix provides a set of algorithms required for these calculations.

Non-equilibrium ion-(polar) molecule reaction rate coefficients

1985 ◽  
Vol 28 (2) ◽  
pp. 353-357 ◽  
Author(s):  
R. Schmidt ◽  
R. Schuster ◽  
W. Stiller
Keyword(s):  
Reaction Rate ◽  
Polar Molecule ◽  
Rate Coefficients ◽  
Molecule Reaction ◽  
Non Equilibrium

Reactivity Trends in the Gas Phase Addition of Acetylene to N-protonated Aryl Radical Cations

2020 ◽  
Author(s):  
Oisin Shiels ◽  
P. D. Kelly ◽  
Cameron C. Bright ◽  
Berwyck L. J. Poad ◽  
Stephen Blanksby ◽  
...  
Keyword(s):  
Gas Phase ◽  
Ion Trap ◽  
Radical Cations ◽  
Rate Coefficients ◽  
Similar Process ◽  
Ion Molecule Reactions ◽  
Aromatic Radicals ◽  
Polycyclic Aromatic ◽  
Gas Phase Ion ◽  
Type Radical

<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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