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Abstract
A model Hamiltonian for the reaction CH4+ > CH3+ + H, parametrized to exhibit either early or late inner transition states, is employed to investigate the dynamical characteristics of the roaming mechanism. Tight/loose transition states and conventional/roaming reaction pathways are identified in terms of timeinvariant objects in phase space. These are dividing surfaces associated with normally hyperbolic invariant manifolds (NHIMs). For systems with two degrees of freedom NHIMS are unstable periodic orbits which, in conjunction with their stable and unstable manifolds, unambiguously define the (locally) nonrecrossing dividing surfaces assumed in statistical theories of reaction rates. By constructing periodic orbit continuation/bifurcation diagrams for two values of the potential function parameter corresponding to late and early transition states, respectively, and using the total energy as another parameter, we dynamically assign different regions of phase space to reactants and products as well as to conventional and roaming reaction pathways. The classical dynamics of the system are investigated by uniformly sampling trajectory initial conditions on the dividing surfaces. Trajectories are classified into four different categories: direct reactive and nonreactive trajectories, which lead to the formation of molecular and radical products respectively, and roaming reactive and nonreactive orbiting trajectories, which represent alternative pathways to form molecular and radical products. By analysing gap time distributions at several energies, we demonstrate that the phase space structure of the roaming region, which is strongly influenced by nonlinear resonances between the two degrees of freedom, results in nonexponential (nonstatistical) decay. (C) 2014 AIP Publishing LLC.
Original language  English 

Article number  134112 
Number of pages  17 
Journal  Journal of Chemical Physics 
Volume  140 
Issue number  13 
DOIs  
Publication status  Published  7 Apr 2014 
Keywords
 TRANSITIONSTATE THEORY
 UNIMOLECULAR REACTIONS
 NUCLEOPHILICSUBSTITUTION
 ISOMERIZATION DYNAMICS
 BIMOLECULAR COLLISIONS
 ASYMPTOTIC STABILITY
 TRAPPED TRAJECTORIES
 HAMILTONIANSYSTEMS
 DISSOCIATION RATES
 CLASSICAL THEORIES
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Dive into the research topics of 'Roaming dynamics in ionmolecule reactions: phase space reaction pathways and geometrical interpretation'. Together they form a unique fingerprint.Projects
 1 Finished

NonStatistically, Selectivity and Phase Space Structure in Organic Reactions
1/01/13 → 1/01/16
Project: Research
Profiles

Professor Stephen R Wiggins
 School of Mathematics  Professor of Applied Mathematics
 Fluids and materials
 Applied Mathematics
Person: Academic , Member