Thermochemical properties of small oxygenated sulfur hydrocarbons and kinetics - reaction pathways of methylthiomethyl radical with oxygen
Department of Chemistry and Environmental Science
Master of Science
Bozzelli, Joseph W.
Krasnoperov, Lev N.
Gund, Tamara M.
The thermochemical properties on CH3SCH2OOH and the corresponding two radicals resulting from loss of H atom: CH3SCH2OO and CH2SCH2OOH are important to understand the stability, reaction paths and kinetics of reactions of dimethyl sulfide and other sulfur hydrocarbons (sulfides) in the atmosphere and combustion processes. Thermochemical properties for species and transition states in the methylthiomethyl radical (CH3SCH2) + O2 reaction system are analyzed to evaluate reaction paths and kinetics under these conditions. Isodesmic working reaction are employed to determine the enthalpies of formation (ΔHf°298) using density functional (B3LYP/6-3 1 1G(d,p)) and complete basis set extrapolation (CBS-QB3) computational methods. Entropy (S°298) and heat capacities CP(T) ( 300≤T/K≤1500) are determined using geometric parameters and vibration frequencies obtained at B3LYP/6-3 11 G(d,p) level of calculation. Quantum Rice-Ramsperger-Kassel(QRRK) analysis is used to calculate energy- dependent rate constants, k(E) and master equation is used to account for collisional stabilization of adduct and isomer. The methyithiomethyl radical adds to oxygen to form a methylperoxy racial with a 37.82 kcal/mol well depth. The peroxy radical can undergo dissociation back to reactants, isomerize via hydrogen shift (TS1, Ea=17.06kcal/mol) to form a hydroperoxide methyl radical CH2SCH2OOH, decompose via hydrogen transfer (TS2, Ea=37.79kcal/mol) to form CH3SC(=O)H plus OH radical , or the peroxy radical can also attack the sulfur atom via TS3 (Ea=32.92kcal/mol) to form CH3S(=O) + CH2O. The CH2SCH2OOH isomer can decompose via TS4 (Ea=24.O9kcal/mol) to form CH2O+CH2S+OH, or through a four-member ring transition state (TS5, Ea= 30.77kcal/mol) to form 1,3-Oxathietane + OH.
Structures and thermochemical properties on Sulfenic Acids (RSOH R = CH3, CH3CH2, CH2=CH,) and their radicals are determined by CBS-QB3 calculation. Molecular structures and vibration frequencies are calculated at B3LYP/6-311G(d,p) levels. ΔHF°298, S°298 and C(T) for the concerned species are calculated in this study. Enthalpies of formation are determined using the ΔH°rxn(298) and known enthalpies in each of different working reactions. Contributions to entropy and heat capacity from internal rotation are also determined.
njit-etd2004-130 (90 pages ~ 3,442 KB pdf)
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Created November 13, 2008