Hydrogen physisorption on the (BeO)n, B2H4(Be,Ti), and B6Ti3 metal clusters: a computational study of energies and atomic charges.

The equilibrium structures of BeO clusters and Be,Ti-decorated boranes were computed with the ωB97X-D method and the 6-31G + (2d,2p) and aug-cc-pVTZ basis sets to study their intermolecular interactions with hydrogen molecules. Thermochemical and molecular properties such as the harmonic vibrational frequency, dipole and quadrupole moments, and atomic charges are employed to understand the attractive interactions that control the adsorption process. Comparison of molecular properties and atomic charges of the studied compounds before and after H2 molecule adsorption shows that most of the interactions among the BeO clusters and boranes with H2 molecules constitute a combination of dispersion, electrostatic, and weak charge transfer interactions. Calculated values of Hirschfeld atomic charges and ΔEe (in parenthesis) (BeO)4.8H2 (0.028 e and -2.0 kcal.mol-1), (BeO)2.12H2 (0.030 e and -2.8 kcal.mol-1), B6Ti3.10H2 (0.045 e and -15.4 kcal.mol-1), and B6Ti3+.10H2 (0.058 e and -15.3 kcal.mol-1) show qualitative correlation between hydrogen atomic charges and electronic energy of hydrogen interaction. The ωB97X-D/6-31 + G(2d,2p) values of Gibbs free energy at 298.15 K for (BeO)4.8H2 B2H4Ti.4H2 and B6Ti3.10H2 clusters are equal to -5.0, -4.9, and -5.1 kcal.mol-1, respectively, which are within the range of energy parameters of materials that could be employed in hydrogen storage tanks for light vehicles.

Effects of multidimensional tunneling in the kinetics of hydrogen abstraction reactions of O (3 P) with CH3 OCHO.

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-CH3 OCHO by O (3 P) giving CH3 OCO + OH (R1) and CH2 OCHO + OH (R2). The structures and electronic energies are computed with the M06-2X method. Benchmark calculations with the CBSD-T 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 × 10-15 cm3 molecule-1 s-1 which agrees well with experiment value of 9.3 × 10-15 cm3 molecule-1 s-1 (Mori, Bull. Inst. Chem. Res. 1981, 59, 116). © 2018 Wiley Periodicals, Inc.