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Abstract: Geometries, energies, frequencies, and rate constants of the reaction F (2P)+C2H6 →C2H5 +HF were computed using the MP2 and CCSD(T) approaches, correlation-consistent basis sets, and an extrapolation scheme to assess the complete basis set (CBS) limit energies. Values of the enthalpy of reaction at 0K calculated with the CCSD(T)/cc-pVQZ method and extrapolated to the CBS limit are equal to −35.2 and −36.7kcal/mol, respectively (Exp. −35.3±0.5kcal/mol). Rate constants calculated with the zero-order interpolated variational transition state (IVTST-0) method are in good agreement with experiment. [Copyright &y& Elsevier]

Abstract: Geometries, frequencies, energies, and rate constants of the reaction N(4S)+CH4 →NH+CH3 were computed using coupled-cluster theory, correlation-consistent basis sets, and extrapolations schemes to assess the complete basis set limit energies. Our best calculation gives a classical barrier height and reaction energy of 32.9 and 29.3kcal/mol, respectively, and 24.6kcal/mol for the reaction enthalpy (. Thermal (200–2000K) rate constants were calculated with the canonical variational transition state theory, and indicate a very slow reaction when compared with the ones with N(2D) and N(2P). Using the CVT/μOMT method, the value of H/D KIE is 6.3 (300K). [Copyright &y& Elsevier]

Abstract: The CH4 +F(2P)→CH3 +HF abstraction reaction was investigated using the BH&HLYP, MP2, and CCSD(T) approaches, and two series of correlation consistent basis sets. At the CCSD(T)/cc-pVTZ level, the classical barrier height (ΔV #), and the vibrationally adiabatic ground-state barrier height () are equal to 1.8 and 0.5kcal/mol, respectively. CCSD(T)/cc-pVQZ calculations give a value for the enthalpy of reaction at 0K () of −31.5kcal/mol (Expt. −32.1kcal/mol). Rate constants calculated with the zero-order interpolated variational transition state (IVTST-0) method are in agreement with experiment. The activation energy computed as local two-points slopes of Arrhenius plots in the temperature range of 200–400K, equal to 0.59kcal/mol, is also in good agreement with experiment (0.53kcal/mol). [Copyright &y& Elsevier]

Abstract: Kinetic isotope effects (KIE) for hydrogen abstraction from CH4, CD4, and 13CH4 by fluorine was studied by the variational transition state theory with multidimensional tunneling contributions (VTST/MT). A low-level potential energy surface is obtained with the AM1SRP method. High-level energies, geometries and frequencies of the reactants, transition state, and products were computed using MP2 and CCSD(T) methods. Using the CVT/μOMT method, the kH/kD kinetic isotope effect value is 1.52 (298K), in excellent agreement with experimental values (1.4–1.5). All computed values of k12C/k13C KIE over a large range of temperatures (200–2000K) show normal values (KIE>1). [Copyright &y& Elsevier]

Accurate potential energy curves, transition moments, spectroscopic constants, radiative transition probabilities, and lifetimes for the states X 3Σ-, (1) 3Π, and (2) 3Σ- of BeC, MgC, and CaC are reported using high level calculations. Diagonal transitions dominate for the (2) 3Σ- → X 3Σ- system, with band origins falling at 745, 648, and 770 nm, and an intensity ratio of 6,3,1, respectively for BeC, MgC, and CaC. Radiative lifetimes for v′=0 are equal to 0.48, 1.45, and 3.29 μs for the state (2) 3Σ-, and equal to 13.57, 10.44, and 9.62 μs for the state (1) 3Π for BeC, MgC, and CaC. [Copyright &y& Elsevier]

Electronic energies, geometries, and harmonic vibration frequencies for the reactants, products, and transition state for the Cl(3P)+C2H6→C2H5+HCl abstraction reaction were evaluated at the HF and MP2 levels using several correlation consistent polarized-valence basis sets. Single-point calculations at PMP2, MP4, QCISD(T), and CCSD(T) levels were also carried out. The values of the forward activation energies obtained at the MP4/cc-pVTZ, QCISD(T)/cc-pVTZ, and CCSD(T)/cc-pVTZ levels using the MP2/cc-pVTZ structures are equal to −0.1, −0.4, and −0.3 kcal/mol, respectively. The experimental value is equal to 0.3±0.2 kcal/mol. We found that the MP2/aug-cc-pVTZ adiabatic vibration energy for the reaction (−2.4 kcal/mol) agrees well with the experimental value −(2.2–2.6) kcal/mol. Rate constants calculated with the zeroth-order interpolated variational transition state (IVTST-0) method are in good agreement with experiment. In general, the theoretical rate constants differ from experiment by, at most, a factor of 2.6. [Copyright &y& Elsevier]

Accurate optimized equilibrium geometries, harmonic frequencies and rotational constants of the gauche conform (C2 symmetry) of hydrazine (N2H4) have been calculated employing a large series of basis sets and several ab initio methods. Our best estimate computed equilibrium geometries are rNN=1.434 A˚, rNHi=1.013 A˚, rNHo=1.010 A˚, θNNHi=111.3°, θNNHo=106.8° and θHiNNHo=89.7°. These predictions were used as reference in the analysis of the experimental and theoretical data, and we expected that the present results could guide future investigations in this direction. [Copyright &y& Elsevier]

Highlights: [•] Thermochemical and kinetics parameters for the H abstraction reaction S(3P)+CH4 →CH3 +SH(2Π). [•] CCSD(T) and DFT geometries, energies, and vibrational frequencies of the stationary states. [•] Reactional paths of the S(3P)+CH4 reaction calculated with M05/MG3S method. [•] Thermal rate constants (200–2000K) using VTST/MT theory. [ABSTRACT FROM AUTHOR]

Abstract: Equilibrium geometries, harmonic vibrational frequencies of the C2h and D2h conformers of the hydrazine ion (N2H4 +) were calculated with the CCSD(T) method, in combination with the correlation consistent basis sets of Dunning. Valence and all electron correlation calculations were also carried out using the correlation consistent core and valence polarization triple-zeta basis set (cc-pCVTZ). The adiabatic ionization potential of hydrazine were also calculated using CCSD(T) and CASSCF/MRCI with the CBS extrapolation with the best results respectively equal to 8.07 and 7.81eV, which are closer to experimental data, equal to 8.1±0.15 eV. [Copyright &y& Elsevier]

• Identification and quantification of soot precursors by quantum chemistry approach. • Sub-mechanism containing hydrogen abstraction and beta-scission reactions. • Kinetic parameters for several alkane elementary reactions. • Farnesane produces ten times lower soot precursors than n -dodecane. The worldwide increase concern about the use of fossil fuels is causing a running for the development of green fuels, trying to slow down the emissions of soot and greenhouse gases. Recent studies are pointing up that branched carbon chain structures of alkanes, terpenoids, and sesquiterpenes produce less soot during combustion, they have been employed as an additive in diesel/kerosene engines. In this work, a decomposition sub-mechanism of farnesane and n -dodecane fuels was studied, using the calculated Arrhenius parameters for several hydrogen abstractions and β -scission elementary reactions to compare the preceding species of the soot precursors. The calculations were carried out using density functional theory to obtain the thermochemical properties of all molecules and transition state theory to calculate the thermal rate coefficients. The results showed the importance of the thermochemical analysis in choosing the appropriate temperature range for the selected reactions, to obtain a qualitatively appropriate set of kinetic parameters. The molar fraction comparison resulting from the sub-mechanism of the two fuels revealed that farnesane yields a smaller amount of species necessary to produce soot precursors due to the position of the branched carbons. The methodology used here allows the construction of additive mechanisms and can be used to aid the design of new fuels that could be more efficient and/or less polluting. By investigating, for example, the first steps of a fuel decomposition in a reduced mechanism, avoiding the complexity of a complete mechanism, while also generating fairly accurate kinetic parameters for elementary reactions. [ABSTRACT FROM AUTHOR]

Accurate potential energy curves, dissociation energies, and molecular constants for several low-lying singlet and triplet electronic states of AsCl were investigated using the CASSCF/MRCI methodology, including the spin–orbit splitting with the aug-cc-pV5Z-DK basis set. Our results represent an improvement over previous the theoretical descriptions for the lowest lying states, as well as characterize another higher excited state not previously investigated. Transition probabilities and radiative lifetimes for the (1) 3 Π → X 3 Σ − band system were also predicted using Einstein spontaneous emission coefficients. [ABSTRACT FROM AUTHOR]

Highlights: [•] Low-lying electronic states of the GeB molecule. [•] Spin–orbit states. [•] Molecular constants. [•] Transition probabilities. [ABSTRACT FROM AUTHOR]

Highlights: [•] Accurate structures of aluminum clusters: Al n x (n =1–9, x =0, ±1). [•] Electron affinities and ionization potential. [•] DFT and CCSD(T) electronic calculations. [ABSTRACT FROM AUTHOR]

Abstract: The lowest singlet and triplet states of AlP3, GaP3 and BP3 molecules with Cs, C2v and C3v symmetries were characterized using the B3LYP functional and the aug-cc-pVTZ and aug-cc-pVQZ correlated consistent basis sets. Geometrical parameters and vibrational frequencies were calculated and compared to existent experimental and theoretical data. Relative energies were obtained with single point CCSD(T) calculations using the aug-cc-pVTZ, aug-cc-pVQZ and aug-cc-pV5Z basis sets, and then extrapolating to the complete basis set (CBS) limit. [Copyright &y& Elsevier]

Abstract: Barrier heights, structures, reaction energies, and rate constants are calculated with the DFT, MP2, and CCSD(T) methods for the first two channels of the H+CH3OH reactions. The best estimate results based on CCSD(T) calculations give reaction enthalpies () for the first (−8.4kcal/mol) and second (0.8kcal/mol) reactive channels, which are comparable to the experimental values, −8.8±0.9 and −0.3±0.9kcal/mol, respectively. Rate constants and activation energies calculated with the IVTST-0 method using CCSD(T)/cc-pVTZ geometries and frequencies are also in excellent agreement with experiment data. [Copyright &y& Elsevier]