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In this work, we have performed Raman scattering measurements in Ba 2 BiSbO 6 ceramics in the temperature range from 10 to 573 K. The Raman spectra were examined using group theory to analyze the decomposition of the reducible representation of the vibrational modes and with a virtual octahedral model. At room temperature, five modes were observed. At low temperatures, the spectra subtly showed the rhombohedral-monoclinic phase transition, which was identified by changes in the Raman intensity of the bending and symmetrical stretching SbO 6 octahedral modes. The cubic-rhombohedral phase transition was not clearly evident in the high-temperature Raman data.

Density functional theory (DFT) geometries, vibrational frequencies, barrier heights, and reaction energies are computed for the first reactive channels of reactions involving the hydrogen atoms with CH 3 OH and C 2 H 5 OH. For both reactions, the density functional BB1K specially fitted to study hydrogen abstraction reactions was able to give barrier heights and reaction enthalpies at 0 K with accuracy close to 1.0 kcal/mol. The B3LYP systematically underestimate the classical barrier heights and predict reasonable values for the geometries and frequencies of CH 3 OH and C 2 H 5 OH. The results show that the studied DFTs have strengths and weaknesses which are somewhat complementary.

DFT methods are used in calculations of geometries, energies, and frequencies for O ( 3 P) þ CH 3 OH reactions. CCSD(T) single-point calculations are carried out followed by extrapolation to the complete basis set (CBS) limit and inclusion of core correlation. The best estimate results of the reaction enthalpies (DH 0 0 ) for the first (À7.1 kcal/mol), second (2.0 kcal/mol), and the third (25.8 kcal/mol) reactions path are in excellent agreement with the experimental values, i.e., À7.2 6 0.2, 1.2 6 1.0, and 26.0 6 1.2 kcal/mol, respectively. Rate constants and activation energies in the range of 300-2,000 K calculated with the variational transition state theory are in good agreement with previous studies. H/D and 12 C/ 13 C kinetic isotope effects are also calculated in good agreement with available experimental data.

The abstraction and addition reactions of H with trans-N(2)H(2) are studied by high-level ab initio methods and density functional theory. Rate constants were calculated for these two reactions by multistructural variational transition state theory with multidimensional tunneling and including torsional anharmonicity by the multistructural torsion method. Rate constants of the abstraction reaction show large variational effects, that is, the variational transition state yields a smaller rate constant than the conventional transition state; this results from the fact that the variational transition state has a higher zero-point vibrational energy than the conventional transition state. The addition reaction has a classical barrier height that is about 1 kcal∕mol lower than that of the abstraction reaction, but the addition rates are lower than the abstraction rates due to vibrational adiabaticity. The calculated branching ratio of abstraction to addition is 3.5 at 200 K and decreases to 1.2 at 1000 K and 1.06 at 1500 K.

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Quantum tunneling paths are important in reactions when there is a significant component of hydrogenic motion along the potential energy surface. In this study, variational transition state with multidimensional tunneling corrections are employed in the calculations of the thermal rate constants for hydrogen abstraction from the cis-CH OCHO by O ( P) giving CH OCO + OH (R1) and CH OCHO + OH (R2). The structures and electronic energies are computed with the M06-2X method. Benchmark calculations with the CBS approach give an enthalpy of reaction at 0 K for R1 (-2.8 kcal/mol) and R2 (-2.5 kcal/mol) which are in good agreement with the experiment, i.e. -2.61 and -1.81 kcal/mol. At the low and intermediate values of temperatures, small- and large-curvature tunneling dominate the kinetics of R1, which is the dominant path over the range of temperature from 250 to 1200 K. This study shows the importance of multidimensional tunneling corrections for both R1 and R2, for which the total rate constant at 298 K calculated with the CVT/μOMT method is 8.2 × 10 cm molecule s which agrees well with experiment value of 9.3 × 10 cm molecule s (Mori, Bull. Inst. Chem. Res. 1981, 59, 116). © 2018 Wiley Periodicals, Inc.