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An initio calculations of the potential energy surface for the reaction of the tricarbon with acetylene were performed at the RCCSD(T)/cc-pVQZ/B3LYP/6-311G(d,p)+ZPE[B3LYP/6-311G(d,p) level. The results show that this reaction starts from the formation of the 30(didehydrovinylidene)cyclopropene intermediate i1 or the five-member ring structure i7.

The potential energy surface for the reaction of C6H5 with O2 is investigated by performing Ab initio GM calculations. However, since C6H5O + O and C5H5 + CO2 are expected to be the major primary products of the C6H5 + O2 reaction and thermal decomposition of C6H5O leads to C5H5 + C, cyclopentadienyl radical are likely to be the major product of phenyl radical oxidation.

Photo-oxidation of amino acids is known to generate reactive protein radicals that lead to lethal disorders. We investigated photoionization of hydrated phenylglycine complexes in the gas phase and found that the excess internal energy from photoionization drives decarboxylation in competition with dehydration. We also found that, in decarboxylation, the solvent migrates a large distance from the C terminus of the neutral amino acid to the N terminus of the newly formed radical cation upon ionization, prior to the departure of the carboxyl group. It is noted that a solvent does not just act as a passive medium bound to the solute molecule but actively pursues its own course of action upon external perturbation that changes its chemical environment. [ABSTRACT FROM AUTHOR]

Ab initio calculations of the potential energy surface for the C3(1g) C2H2(1g) reaction have been performed at the RCCSD(T)/cc-pVQZ//B3LYP/6-311G(d,p) ZPEB3LYP/6-311G(d,p) level with extrapolation to the complete basis set limit for key intermediates and products. These calculations have been followed by statistical calculations of reaction rate constants and product branching ratios. The results show the reaction to begin with the formation of the 3-(didehydrovinylidene)cyclopropene intermediate i1or five-member ring isomer i7with the entrance barriers of 7.6 and 13.8 kcal/mol, respectively. i1rearranges to the other C5H2isomers, including ethynylpropadienylidene i2, singlet pentadiynylidene i3, pentatetraenylidene i4, ethynylcyclopropenylidene i5, and four- and five-member ring structures i6, i7, and i8by ring-closure and ring-opening processes and hydrogen migrations. i2, i3, and i4lose a hydrogen atom to produce the most stable linear isomer of C5H with the overall reaction endothermicity of ∼24 kcal/mol. H elimination from i5leads to the formation of the cyclic C5H isomer, HC2C3, H, 27 kcal/ mol above C3C2H2. 1,1-H2loss from i4results in the linear pentacarbon C5H2products endothermic by 4 kcal/mol. The H elimination pathways occur without exit barriers, whereas the H2loss from i4proceeds via a tight transition state 26.4 kcal/mol above the reactants. The characteristic energy threshold for the reaction under single collision conditions is predicted be in the range of ∼24 kcal/mol. Product branching ratios obtained by solving kinetic equations with individual rate constants calculated using RRKM and VTST theories for collision energies between 25 and 35 kcal/mol show that l-C5H H are the dominant reaction products, whereas HC2C3H and l-C5H2are minor products with branching ratios not exceeding 2.5% and 0.7%, respectively. The ethynylcyclopropenylidene isomer i5is calculated to be the most stable C5H2species, more favorable than triplet pentadiynylidene i3tby ∼2 kcal/mol. [ABSTRACT FROM AUTHOR]

HOSO[sub 2] radical is the key intermediate for the oxidation SO[sub 2] to SO[sub 3] by OH radical in the atmosphere. The structural aspects and the energetics of the reaction HOSO[sub 2]+O[sub 2]→SO[sub 3]+HO[sub 2] have been studied using Mo\ller-Plesset (MP2) and density functional (DFT) techniques with 6-31G[sup **] and triple-ζ, quadruple-ζ, and quintuple-ζ quality basis sets including diffuse basis functions. The detailed theoretical analyses have further revealed that this reaction could proceed through the formation of intermediate complexes and an intramolecular proton transfer like transition state. The energetics of these intermediate reactions has been studied in detail. The use of MP2 methods to study such radical mechanisms had some characteristic symmetry-breaking problem with larger basis sets. This unphysical situation with larger basis set MP2 calculations in this hypervalent system has been explained through the interpretation of the relevant energy surface. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]