Jee Hwan Jang

A theoretical investigation of the nature of the π-H interaction in ethene–H2O, benzene–H2O, and benzene–(H2O)2

We have carried out a detailed investigation of the nature of the π-H interaction in the ethene–H2O, benzene–H2O, and benzene–(H2O)2 complexes using large basis sets (ranging from 6-31+G* to TZ2P++) and high levels of theory. The minimum geometries, and hence the vibrational frequencies, of all the complexes have been obtained at the second order Mo/ller–Plesset (MP2) level of theory. The binding energy of the ethene–H2O complex is only about 1 kcal/mol lower than that of the benzene–H2O complex. In the benzene–(H2O)2 complex, the interaction of benzene with the π-bonded water to that with the second water is nearly equivalent. In order to explain the above interesting facets of the interaction of water with benzene and ethene, the interaction energies were decomposed into the individual interaction energy components using the recently developed symmetry adapted perturbation theory (SAPT) program. The SAPT results indicate that the repulsive exchange energies play a crucial role in governing the energies ...

Quantum mechanical probabilistic structure of the benzene-water complex

Abstract On the realistic energy hypersurface of the floppy benzene-water complex obtained with high-levels of ab inition theory, the experimental structure, rotational constants and binding energy cannot be described simply in terms of the equilibrium position, but need to be characterized in a quantum mechanical probabilistic way. In this way, the structure and rotational constants show excellent agreement with experiment, and the binding energy is in favor of the experimental upper bound. The most important component of the benzene-water binding energy is the electron correlation, followed by the interaction between the water dipole and benzene quadrupole.

Hydrogen bonding between the water molecule and the hydroxyl radical (H2O⋅OH): The 2A‘ and 2A’ minima

The two degenerate components of the OH radical 2Π ground electronic state give rise to independent minima (of 2A‘ and 2A’ symmetries) upon interaction with the water molecule. These two minima have been investigated here for the first time using ab initio quantum mechanical methods. Minimum, double zeta, double zeta plus polarization, and triple zeta plus double polarization basis sets have been employed in conjunction with self‐consistent‐field, second‐order perturbation, and configuration interaction methods. At all levels of theory, the 2A‘ state is predicted to be the global minimum, with a dissociation energy De of about 3.5 kcal/mol. The 2A’ state is predicted to lie about 1 kcal higher in energy. Both minima occur for structures with OH⋅⋅⋅O linkages close to linear and are reminiscent of the water dimer. However, the H⋅⋅⋅O distances (∼2.1 A for 2A‘, ∼2.2 A for 2A’) are significantly longer than observed for the water dimer. Preliminary estimates of the H2O⋅OH vibrational frequencies are made.

Thermal impedance spectroscopy for Li-ion batteries using heat-pulse response analysis

Abstract Novel characterization of the thermal properties of batteries have been introduced by defining their frequency-dependent thermal impedance functions. The thermal impedance function can be approximated as a thermal impedance spectrum by analyzing the experimental temperature transient which is related to the thermal impedance function through Laplace transformation. In order to obtain the temperature transient, a process has been devised to generate an external heat pulse with heating wire and to measure the response of the battery. This process is used to study several commercial Li-ion batteries of cylindrical type. Thermal impedance measurements have been performed using a potentiostat/galvanostat controlled by a digital signal processor, which is more commonly available than a flow-meter usually applied for thermal property measurements. Thermal impedance spectra obtained for batteries produced by different manufacturers are found to differ considerably. Comparison of spectra at different states-of-charge indicates an independence of the thermal impedance on the charge state of the battery. It is shown that the thermal impedance spectrum can be used to obtain simultaneously the thermal capacity and the thermal conductivity of the battery by non-linear complex least-squares fit of the spectrum to the thermal impedance model.

Potential new high energy density materials: Cyclooctaoxygen O8, including comparisons with the well‐known cyclo‐S8 molecule

The cyclic O8 molecule has been studied using ab initio quantum mechanical methods. Molecular structures were fully optimized at levels of theory up to and including second‐order perturbation theory (MP2) using a double zeta plus polarization basis set. Parallel theoretical studies were carried out for the valance isoelectronic S8 molecule, for which much experimental data exists. With double zeta plus polarization (DZ+P) self‐consistent‐field (SCF) theory vibrational frequencies and infrared and Raman intensities have been predicted. Cyclo‐O8 is considerably more stable than experimental O–O bond energies would suggest and is predicted to lie only 94 kcal/mol above four infinitely separated O2 molecules.

Sulfur clusters: structure, infrared, and Raman spectra of cyclo-S6 and comparison with the hypothetical cyclo-O6 molecule

Ab initio quantum mechanical methods have been applied to the S6 and O6 molecules at their respective D3d hexagonal chair equilibrium geometries. Double zeta plus polarization (DZ + P) and triple zeta plus double polarization (TZ + 2P) basis sets have been used in conjunction with the self-consistent field (SCF) method and second-order perturbation theory. Equilibrium geometries, harmonic vibrational frequencies, infrared intensities, and Raman intensities have been predicted for the two cyclic molecules. Two previous vibrational difficulties between theory and experiment for S6 have been resolved. The O6 molecule appears to be similar to the well-characterized S6 in several respects. However, its dissociation energy and vibrational frequencies reveal a much flatter potential energy surface for O6 in the region of the equilibrium geometry. While still predicted to correspond to a genuine potential minimum, O6 nevertheless lies about 100 kcal mol-1 above three separated O2 molecules. From a methodological ...