An Application of Conventional Transition State Theory To Compute High-Pressure Limit Thermal Rate Coefficients for the Reaction: H(D) + O2 .dblharw. H(D)O*2 .dblharw. OH(D) + O

1994 ◽  
Vol 98 (42) ◽  
pp. 10794-10801 ◽  
Author(s):  
Ronald J. Duchovic ◽  
J. David Pettigrew
Keyword(s):  
High Pressure ◽  
Transition State ◽  
Transition State Theory ◽  
State Theory ◽  
Rate Coefficients ◽  
Pressure Limit

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.

scholarly journals Pressure-Dependent Kinetics of Peroxy Radicals Formed in Isobutanol Combustion

2020 ◽  
Author(s):  
Mark Goldman ◽  
Nathan Wa-Wai Yee ◽  
Jesse Kroll ◽  
William H. Green
Keyword(s):  
High Pressure ◽  
Reaction Rates ◽  
State Theory ◽  
Rate Coefficients ◽  
Quantum Calculations ◽  
Peroxy Radicals ◽  
Alkoxy Radical ◽  
Pressure Limit ◽  
Combustion Properties ◽  
Quantum Chemistry Calculations

Bio-derived isobutanol has been approved as a gasoline additive in the U.S., but our understanding of its combustion chemistry still has significant uncertainties. Detailed quantum calculations could improve model accuracy leading to better estimation of isobutanol’s combustion properties and its environmental impacts. This work examines 47 molecules and 38 reactions involved in the first oxygen addition to isobutanol’s three alkyl radicals located α, β, and γ to the hydroxide. Quantum calculations are mostly done at CCSD(T)-F12/cc-pVTZ-F12//B3LYP/CBSB7, with 1-D hindered rotor corrections obtained at B3LYP/6-31G(d). The resulting potential energy surfaces are the most comprehensive isobutanol peroxy networks published to date. Canonical transition state theory and a 1-D microcanonical master equation are used to derive high-pressure-limit and pressure-dependent rate coefficients, respectively. At all conditions studied, the recombination of α- isobutanol radical with O2 forms HO2 and isobutanal. The recombination of γ-isobutanol radical with O2 forms a stabilized hydroperoxy alkyl radical below 400 K, water and an alkoxy radical at higher temperatures, and HO2 and an alkene above 1200 K. The recombination of β-isobutanol radical with O2 results in a mixture of products between 700-1100 K, forming acetone, formaldehyde and OH at lower temperatures and forming HO2 and alkenes at higher temperatures. The barrier heights, high-pressure-limit rates, and pressure-dependent kinetics generally agree with the results from previous quantum chemistry calculations. Six reaction rates in this work deviate by over three orders of magnitude from kinetics in detailed models of isobutanol combustion, suggesting the rates calculated here can help improve modeling of isobutanol combustion and its environmental fate.

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