CAS(14,12)/cc-pvdz calculations are reported for the reaction of 3CH2+3O2fproducts. On the singlet potential energy surface, a transition state has been located with an energy barrier of 1.65kcal/mol, which is in good agreement with the experimental estimation of 1.0-1.5kcal/mol. The rearrangement and metathesis of the singlet intermediates have been also investigated at the same level of theory. For the triplet case, the formation of CH2OO has an energy barrier of 5.79kcal/mol, and the formed triplet CH2OO could be further decomposed into CH2O+O(3P) with an energy barrier of 2.92kcal/mol. The geometries of some key points have been relocated at the CAS (8,6)+1+2/cc-pvdz level of theory for comparison. The present theoretical results for the total reaction rates, at the CAS (8, 6)+1+2/cc-pvdz level, can be expressed by the three-parameter expression: k(T)) 4.273 10-18T2.245exp (-185/T) within (5% error at the temperature range 295-2600K.

This paper uses the properties of atom X enclosed within an adamantane cage, denoted by X@C10H16, as a vehicle to introduce the Ehrenfest force into the discussion of bonding, the properties being determined by the physics of an open system. This is the force acting on an atom in a molecule and determining the potential energy appearing in Slater's molecular virial theorem. The Ehrenfest force acting across the interatomic surface of a bonded pair atomssatoms linked by a bond pathsis attractive, each atom being drawn toward the other, and the associated surface virial that measures the contribution to the energy arising from the formation of the surface is stabilizing. It is the Ehrenfest force that determines the adhesive properties of surfaces. The endothermicity of formation for X=He or Ne is not a result of instabilities incurred in the interaction of X with the four methine carbons to which it is bonded, interactions that are stabilizing both in terms of the changes in the atomic energies and in the surface virials. The exothermicity for X=Be2+, B3+, and Al3+ is a consequence of the transfer of electron density from the hydrogen atoms to the carbon and X atoms, the exothermicity increasing with charge transfer despite an increase in the contained volume of X.

Density functional (B3LYP) calculations using the 6-31++g** basis set have been employed to study the title reaction between the cationic 1,3-dipolar 1-aza-2-azoniaallene ion (H2CdN+dNH) and ethene. Our calculations confirmed that [3 + 2] cycloaddition reaction takes place via a threemembered ring intermediate. In addition, solvent effects and substituent effects were also studied. For the reactions involving tetrachloroethene, there are two attacking sites. One is on the NH group in the 1-aza-2-azoniaallene ion, another is on its terminal CH2 group, and they are competitive for both approaching positions. Electron-releasing methyl substituents on ethene favor the reaction, and the potential energy surface is quite different from the previous one.

Density functional (B3LYP) calculations, using the 6-31G** basis set, have been employed to study the title reactions. For the model reaction (H2CdC-NH+dCH2 + H2CdCH2), a complex has been formed with 6.2kcal/mol of stabilization energy and the transition state is 4.0kcal/mol above this complex, but 2.1kcal/mol below the reactants. However, the substituent effects are quite remarkable. When ethene is substituted by electron-withdrawing group CN, the reaction could also yield sixmembered-ring products, but the energy barriers are all more than 7 kcal/mol, which shows that CN group unfavors the reaction. The other substituents, such as CH3O and CH3 groups, have also been considered in the present work, and the results show that they are favorable for the formation of six-membered-ring adducts. The calculated results have been rationalized with frontier orbital interaction and topological analysis.

A combination of high-level quantum-chemical simulations and sophisticated transition state theory analyses is employed in a study of the temperature dependence of the N2H+OH+HNNOH recombination reaction. The implications for the branching between and in the reaction are also explored. The transition N2H+OH N2+H2O NH2+NO state partition function for the recombination reaction is evaluated with a N2H]OH direct implementation of variable reaction coordinate (VRC) transition state theory (TST). The orientation dependent interaction energies are directly determined at the CAS+1+2/cc-pvdz level. Corrections for basis set limitations are obtained via calculations along the cis and trans minimum energy paths employing an Daug-pvtz basis set. The calculated rate constant for the recombination is found N2H+OH+HNNOH to decrease signi-cantly with increasing temperature, in agreement with the predictions of our earlier theoretical study. Conventional transition state theory analyses, employing new coupled cluster estimates for the vibrational frequencies and energies at the saddlepoints along the reaction pathway, are coupled with the VRC-TST analyses for the NH2+NO channels to provide estimates for the branching in the reaction. N2H+OH NH2+NO Modest variations in the exothermicity of the reaction (1-2 kcal mol-1), and in a few of the saddlepoint energies (2-4 kcal mol-1), yield TST based predictions for the branching fraction that are in satisfactory agreement with related experimental results. The unmodi-ed results are in reasonable agreement for higher temperatures, but predict too low a branching ratio near room temperature, as well as too steep an initial rise.