scholarly journals COMPARISON OF 3D CLASSICAL TRAJECTORY AND TRANSITION-STATE THEORY REACTION CROSS SECTIONS.

1971 ◽  
Author(s):  
G W Koeppl ◽  
M Karplus
Keyword(s):  
Transition State ◽  
Cross Sections ◽  
Transition State Theory ◽  
Classical Trajectory ◽  
Reaction Cross ◽  
State Theory ◽  
Reaction Cross Sections

Limitations of Variational Transition State Theory for Barrierless Radical–Radical Recombination Reactions

2004 ◽  
Vol 218 (4) ◽  
pp. 457-468 ◽  
Author(s):  
Jürgen Troe
Keyword(s):  
Transition State ◽  
Transition State Theory ◽  
Classical Trajectory ◽  
State Theory ◽  
Nonadiabatic Dynamics ◽  
Variational Transition State Theory ◽  
Radical Recombination ◽  
Adiabatic Dynamics ◽  
Recombination Reactions ◽  
Variational Transition State

AbstractVariational transition state theory (VTST) is widely used for the modelling of barrierless radical-radical recombination reactions. In this application, VTST suffers from a number of limitations some of which are of more technical, others of more fundamental nature. The former are caused by inappropriate averaging over individual adiabatic channel potentials or by the neglect of quantum effects, the latter are due to deviations from adiabatic dynamics. It is shown that most radical-radical recombination reactions are characterized by Massey parameters which are smaller than unity such that the dynamics is nonadiabatic. VTST treatments which generally assume adiabatic dynamics, therefore, have a fundamental problem. Calculations of rate constants by VTST often exceed classical trajectory results by about 10 to 20percent. This is normally attributed to “recrossing trajectories”. In the present work it is shown, however, that deviations of this magnitude also have to be expected for nonadiabatic dynamics in comparison to adiabatic dynamics. It is, therefore, suggested that “recrossing” at least in part has to be attributed to nonadiabatic dynamics. A way out of the dilemma is the use of a combination of statistical adiabatic channel and classical trajectory concepts.

QUASI-CLASSICAL TRAJECTORY STUDY OF THE REACTION PROBABILITY AND CROSS SECTION OF THE REACTION LiH + H

2013 ◽  
Vol 12 (01) ◽  
pp. 1250093 ◽  
Author(s):  
YULIANG WANG ◽  
JINCHUN ZHANG ◽  
BAOGUO TIAN ◽  
KUN WANG ◽  
XIAORUI LIANG ◽  
...  
Keyword(s):  
Cross Section ◽  
Cross Sections ◽  
Ground State ◽  
Collision Energy ◽  
Energy Surface ◽  
Classical Trajectory ◽  
Reaction Cross ◽  
Reaction Probability ◽  
Title Reaction ◽  
Reaction Cross Sections

Based on the new accurate potential energy surface of the ground state of LiH2 system. Quasi-classical trajectory (QCT) calculations were carried out for the reaction LiH + H . The reaction probability of the title reaction for J = 0 has been calculated. The reaction cross sections were calculated as functions of the collision energy in the range 0.1–2.5 eV. The results were found to be well consistent with the previous real wave packet (RWP) and QCT results.

COMPARATIVE STUDY OF REACTION RATE CONSTANTS FOR THE NH3 + H → NH2 + H2 REACTION WITH GLOBE DYNAMICS AND TRANSITION STATE THEORIES

2009 ◽  
Vol 08 (06) ◽  
pp. 1227-1233 ◽  
Author(s):  
JU LIPING ◽  
LU RUIFENG
Keyword(s):  
Transition State ◽  
Cross Sections ◽  
Rate Constants ◽  
Quantum Dynamics ◽  
Classical Trajectory ◽  
State Theory ◽  
Title Reaction ◽  
Reaction Rate Constants ◽  
Barrier Type ◽  
Good Agreement

The nine-dimension quasi-classical trajectory (QCT) calculations have been carried out for the title reaction with a global potential energy surface (PES) constructed by Corchado and Espinosa-García (J Chem Phys106:4013, 1997). The detailed dynamics calculations cover the specific collision energies falling in the range of 0.62–3.04 eV, which are sufficient to fit the calculated reactive cross-sections into a barrier-type excitation function and to obtain the thermal rate constants. The present QCT rate constants are in good agreement with the recent quantum dynamics (QD) results, both of which are much lower than that of the previous variational transition state theory (VTST).

Microscopic Interpretation of Arrhenius Parameters

2018 ◽  
Author(s):  
Niels Engholm Henriksen ◽  
Flemming Yssing Hansen
Keyword(s):  
Activation Energy ◽  
Transition State ◽  
Transition State Theory ◽  
Average Energy ◽  
Zero Point ◽  
State Theory ◽  
Exponential Factor ◽  
Quantum Tunnelling ◽  
Microscopic Interpretation ◽  
The Difference

This chapter reviews the microscopic interpretation of the pre-exponential factor and the activation energy in rate constant expressions of the Arrhenius form. The pre-exponential factor of apparent unimolecular reactions is, roughly, expected to be of the order of a vibrational frequency, whereas the pre-exponential factor of bimolecular reactions, roughly, is related to the number of collisions per unit time and per unit volume. The activation energy of an elementary reaction can be interpreted as the average energy of the molecules that react minus the average energy of the reactants. Specializing to conventional transition-state theory, the activation energy is related to the classical barrier height of the potential energy surface plus the difference in zero-point energies and average internal energies between the activated complex and the reactants. When quantum tunnelling is included in transition-state theory, the activation energy is reduced, compared to the interpretation given in conventional transition-state theory.

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