Theoretical Studies on the Reaction Path Dynamics and Variational Transition-State Theory Rate Constants of the Hydrogen-Abstraction Reactions of the NH(X3Σ-) Radical with Methane and Ethane

1999 ◽  
Vol 103 (25) ◽  
pp. 4910-4917 ◽  
Author(s):  
Zhen-Feng Xu ◽  
Shen-Min Li ◽  
Yong-Xue Yu ◽  
Ze-Sheng Li ◽  
Chia-Chung Sun
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Transition State Theory ◽  
Reaction Path ◽  
Hydrogen Abstraction ◽  
State Theory ◽  
Theoretical Studies ◽  
Variational Transition State Theory ◽  
Variational Transition State

scholarly journals Association of Cl with C2H2by unified variable-reaction-coordinate and reaction-path variational transition-state theory

2020 ◽  
Vol 117 (11) ◽  
pp. 5610-5616
Author(s):  
Linyao Zhang ◽  
Donald G. Truhlar ◽  
Shaozeng Sun
Keyword(s):  
High Pressure ◽  
Transition State ◽  
Transition State Theory ◽  
Reaction Path ◽  
State Theory ◽  
Reaction Coordinate ◽  
Acetylene Molecule ◽  
Variational Transition State Theory ◽  
Pressure Limit ◽  
Variational Transition State

Barrierless unimolecular association reactions are prominent in atmospheric and combustion mechanisms but are challenging for both experiment and kinetics theory. A key datum for understanding the pressure dependence of association and dissociation reactions is the high-pressure limit, but this is often available experimentally only by extrapolation. Here we calculate the high-pressure limit for the addition of a chlorine atom to acetylene molecule (Cl + C2H2→C2H2Cl). This reaction has outer and inner transition states in series; the outer transition state is barrierless, and it is necessary to use different theoretical frameworks to treat the two kinds of transition state. Here we study the reaction in the high-pressure limit using multifaceted variable-reaction-coordinate variational transition-state theory (VRC-VTST) at the outer transition state and reaction-path variational transition state theory (RP-VTST) at the inner turning point; then we combine the results with the canonical unified statistical (CUS) theory. The calculations are based on a density functional validated against the W3X-L method, which is based on coupled cluster theory with single, double, and triple excitations and a quasiperturbative treatment of connected quadruple excitations [CCSDT(Q)], and the computed rate constants are in good agreement with some of the experimental results. The chlorovinyl (C2H2Cl) adduct has two isomers that are equilibrium structures of a double-well C≡C–H bending potential. Two procedures are used to calculate the vibrational partition function of chlorovinyl; one treats the two isomers separately and the other solves the anharmonic energy levels of the double well. We use these results to calculate the standard-state free energy and equilibrium constant of the reaction.

Computational study on the reaction of atomic chlorine with 1,2-dibromoethane (CH2BrCH2Br)

2013 ◽  
Vol 91 (11) ◽  
pp. 1123-1129 ◽  
Author(s):  
Ang-yang Yu
Keyword(s):  
Transition State ◽  
Rate Constants ◽  
Transition State Theory ◽  
Computational Study ◽  
Minimum Energy ◽  
State Theory ◽  
Basis Set ◽  
Stationary Points ◽  
Variational Transition State Theory ◽  
Variational Transition State

In this work, the reaction mechanism and kinetics of Cl + CH2BrCH2Br → products are theoretically investigated for the first time. The optimized geometries and frequencies of all of the stationary points and selected points along the minimum-energy path for the three hydrogen abstraction channels and two bromine abstraction channels are calculated at the BH&H-LYP level with the 6-311G** basis set and the energy profiles are further calculated at the CCSD(T) level of theory. The rate constants are evaluated using the conventional transition-state theory, the canonical variational transition-state theory, and the canonical variational transition-state theory with a small-curvature tunneling correction over the temperature range 200–1000 K. The results show that reaction channel 3 is the primary channel and the calculated rate constants are in good agreement with available experimental values. The three-parameter Arrhenius expression for the total rate constants over 200–1000 K is provided.

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