The
Waddington mechanism, or the Waddington-type reaction pathway,
is crucial for low-temperature oxidation of both alkenes and alcohols.
In this study, the Waddington mechanism in the oxidation chemistry
of butene and butanol isomers was systematically investigated. Fundamental
quantum chemical calculations were conducted for the rate constants
and thermodynamic properties of the reactions and species in this
mechanism. Calculations were performed using two different
ab initio
solvers: Gaussian 09 and Orca 4.0.0, and two different
kinetic solvers: PAPR and MultiWell, comprehensively. Temperature-
and pressure-dependent rate constants were performed based on the
transition state theory, associated with the Rice Ramsperger Kassel
Marcus and master equation theories. Temperature-dependent thermochemistry
(enthalpies of formation, entropy, and heat capacity) of all major
species was also conducted, based on the statistical thermodynamics.
Of the two types of reaction, dissociation reactions were significantly
faster than isomerization reactions, while the rate constants of both
reactions converged toward higher temperatures. In comparison, between
two
ab initio
solvers, the barrier height difference
among all isomerization and dissociation reactions was about 2 and
0.5 kcal/mol, respectively, resulting in less than 50%, and a factor
of 2–10 differences for the predicted rate coefficients of
the two reaction types, respectively. Comparing the two kinetic solvers,
the rate constants of the isomerization reactions showed less than
a 32% difference, while the rate of one dissociation reaction (P1
↔ WDT12) exhibited 1–2 orders of magnitude discrepancy.
Compared with results from the literature, both reaction rate coefficients
(R4 and R5 reaction systems) and species’ thermochemistry (all
closed shell molecules and open shell radicals R4 and R5) showed good
agreement with the corresponding values obtained from the literature.
All calculated results can be directly used for the chemical kinetic
model development of butene and butanol isomer oxidation.