Thermochemistry reaction paths and oxidation kinetics on ketonyl and aldehydic nitrogen oxides, propene and isooctane: a theoretical study

Thermochemical properties for several atmospheric and combustion related species are determined using computational chemical methods coupled with fundamentals of thermodynamics and statistical mechanics. Enthalpies of formation (ΔHf°298) are determined using isodesmic reaction analysis at the CBS-QB3 composite and the B3LYP density functional methods. Entropies (S°298) and heat capacities (Cp°(T)) are determined using geometric parameters and vibration frequencies; internal rotor contributions are included in S and Cp(T) values in place of torsion frequencies. Kinetic parameters are calculated versus pressure and temperature for the chemical activated formation and unimolecular dissociation. Multi-frequency quantum RRK (QRRK) analysis is used for k(E) with Master Equation analysis for fall off. Recommended values for enthalpies of formation of the most stable conformers of nitroacetone, acetonitrite, nitroacetate and acetyl nitrite are -51.6 kcal mol-1, -51.3 kcal mol-1, -45.4 kcal mol-1 and -58.2 kcal mol-1, respectively. The calculated ΔfH º298 for nitroethylene is 7.6 kcal mol-1 and for vinyl nitrite is 7.2 kcal mol-1. The chemically activated R• + NO2 systems associations proceed to RCO• + NO via chemical activation reaction with a fraction to stabilized adducts and lower energy products at atmospheric pressure and temperature. Thermochemical properties of isooctane (2,2,4-trimethyl pentane) and its four carbon radicals from loss of hydrogen atoms, and kinetics of the tertiary isooctane radical reaction with O2 are determined. The computed standard enthalpy of formation of isooctane from this study is -54.40 kcal mol-1. The major products from reaction of the tert-isooctane radical + O2 to form a chemically activated tert-isooctane-peroxy radical are formation of isooctene plus HO2. Next important products are cyclic ethers plus OH radical. This research is the first fundamentally based study of relevant pathways on the potential energy surfaces of tert-isooctane radicals + O2 using high level composite calculation methods. Kinetic modeling for OH addition to propene and subsequent O2 association to the hydroxyl-propyl radical adduct shows that significant forward reaction goes to regenerate OH radicals over the range of temperature and pressure studied. Recycle of OH from the decomposition of the hydroxyl propyl-peroxy radical is up to 78%. Inclusion of activation energy resulting from OH addition to primary carbon (double activation) does not show increase in OH recycle. The introduction of the rate constants presented in this study into existing reaction mechanisms should lead to better kinetic models for olefin oxidation chemistry the atmospheric