TY - JOUR
T1 - Thermochemical and kinetic analyses on oxidation of isobutenyl radical and 2-hydroperoxymethyl-2-propenyl radical
AU - Zheng, X. L.
AU - Sun, H. Y.
AU - Law, C. K.
PY - 2005/10/13
Y1 - 2005/10/13
N2 - In recognition of the importance of the isobutene oxidation reaction in the preignition chemistry associated with engine knock, the thermochemistry, chemical reaction pathways, and reaction kinetics of the isobutenyl radical oxidation at low to intermediate temperature range were computationally studied, focusing on both the first and the second O 2 addition to the isobutenyl radical. The geometries of reactants, important intermediates, transition states, and products in the isobutenyl radical oxidation system were optimized at the B3LYP/6-311G(d,p) and MP2(full)/6-31G(d) levels, and the thermochemical properties were determined on the basis of ab initio, density functional theory, and statistical mechanics. Enthalpies of formation for several important intermediates were calculated using isodesmic reactions at the DFT and the CBS-QB3 levels. The kinetic analysis of the first O 2 addition to the isobutenyl radical was performed using enthalpies at the CBSQB3 and G3(MP2) levels. The reaction forms a chemically activated isobutenyl peroxy adduct which can be stabilized, dissociate back to reactants, cyclize to cyclic peroxide-alkyl radicals, and isomerize to the 2-hydroperoxymethyl-2-propenyl radical that further undergoes another O 2 addition. The reaction channels for isomerization and cyclization and further dissociation on this second O 2 addition were analyzed using enthalpies at the DFT level with energy corrections based on similar reaction channels for the first O 2 addition. The high-pressure limit rate constants for each reaction channel were determined as functions of temperature by the canonical transition state theory for further kinetic model development.
AB - In recognition of the importance of the isobutene oxidation reaction in the preignition chemistry associated with engine knock, the thermochemistry, chemical reaction pathways, and reaction kinetics of the isobutenyl radical oxidation at low to intermediate temperature range were computationally studied, focusing on both the first and the second O 2 addition to the isobutenyl radical. The geometries of reactants, important intermediates, transition states, and products in the isobutenyl radical oxidation system were optimized at the B3LYP/6-311G(d,p) and MP2(full)/6-31G(d) levels, and the thermochemical properties were determined on the basis of ab initio, density functional theory, and statistical mechanics. Enthalpies of formation for several important intermediates were calculated using isodesmic reactions at the DFT and the CBS-QB3 levels. The kinetic analysis of the first O 2 addition to the isobutenyl radical was performed using enthalpies at the CBSQB3 and G3(MP2) levels. The reaction forms a chemically activated isobutenyl peroxy adduct which can be stabilized, dissociate back to reactants, cyclize to cyclic peroxide-alkyl radicals, and isomerize to the 2-hydroperoxymethyl-2-propenyl radical that further undergoes another O 2 addition. The reaction channels for isomerization and cyclization and further dissociation on this second O 2 addition were analyzed using enthalpies at the DFT level with energy corrections based on similar reaction channels for the first O 2 addition. The high-pressure limit rate constants for each reaction channel were determined as functions of temperature by the canonical transition state theory for further kinetic model development.
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U2 - 10.1021/jp058116a
DO - 10.1021/jp058116a
M3 - Article
C2 - 16332010
AN - SCOPUS:27144453724
SN - 1089-5639
VL - 109
SP - 9044
EP - 9053
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 40
ER -