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A combination of ab initio electronic structure theory, transition state theory and master equation modeling was used to study the kinetics of the reaction CO H[O.sub.2] -> C[O.sub.2] OH. The results have shown that the overall rate coefficient is independent of pressure up to 500 atm for temperature ranging from 300 to 2500 K.

The unimolecular decomposition of ethylene oxide and the oxiranyl radical is examined by molecular orbital calculations, Rice-Ramsperger-Kassel-Marcus (RRKM)/Master Equation analysis, and detailed kinetic modeling of ethylene oxide pyrolysis in a single pulse shock tube. It was found that the largest energy barrier to the decomposition of ethylene oxide lies in its initial isomerization to form acetaldehyde.

The reaction kinetics for gaseous hydroxyl radicals (OH) with deliquesced sodium chloride particles (Na[Cl.sub.aq]) are investigated using a novel experimental technique. The application of this novel method to the reaction of gaseous OH with deliquesced NaCl particles have given a lower limit to the reaction probability of [gamma.sub.net] > = 0.1 with an uncertainty of a factor of 2.

The reaction of C2 with water and the possible subsequent reactions were investigated using ab initio methods. The most feasible reaction following the formation of association intermediate (CCOH2) is the intramolecular hydrogen migration leading to hydroxythyne (HCCOH).

The kinetics of the reaction CO HO2• → CO2•OH was studied using a combination of ab initio electronic structure theory, transition state theory, and master equation modeling. The potential energy surface was examined with the CCSD(T) and CASPT2 methods. The classical energy barriers were found to be about 18 and 19 kcal/mol for CO HO2• addition following the trans and cis paths, respectively. For the cis path, rate constant calculations were carried out with canonical transition state theory. For the trans path, master equation modeling was also employed to examine the pressure dependence. Special attention was paid to the hindered internal rotations of the HOOC•O adduct and transition states. The theoretical analysis shows that the overall rate coefficient is independent of pressure up to 500 atm for temperature ranging from 300 to 2500 K. On the basis of this analysis, we recommend the following rate expression for reaction R1 k(cm3/mol·s) 1.57 × 105T2.18e-9030Tfor 300 ≤ T≤ 2500 K with the uncertainty factor equal to 8, 2, and 1.7 at temperatures of 300, 1000, and 2000 K, respectively. [ABSTRACT FROM AUTHOR]

The reaction kinetics for gaseous hydroxyl radicals (OH) with deliquesced sodium chloride particles (NaClaq) were investigated using a novel experimental approach. The technique utilizes the exposure of substrate-deposited aerosol particles to reactive gases followed by chemical analysis of the particles using computer-controlled scanning electron microscopy with energy-dispersive analysis of X-rays (CCSEM/EDX) capability. Experiments were performed at room temperature and atmospheric pressure with deliquesced NaCl particles in the micron size range at 70−80% RH and with OH concentrations in the range of 1 to 7 × 109cm-3. The apparent, pseudo first-order rate constant for the reaction was determined from measurements of changes in the chloride concentration of individual particles upon reaction with OH as a function of the particle loading on the substrate. Quantitative treatment of the data using a model that incorporates both diffusion and reaction kinetics yields a lower limit to the net reaction probability of net≥ 0.1, with an overall uncertainty of a factor of 2. [ABSTRACT FROM AUTHOR]