Yoo Hang Kim

Collision-induced intramolecular energy flow and C–H bond dissociation in excited toluene

The collision-induced intramolecular energy flow and C–H bond dissociation in toluene have been studied using classical dynamics procedures. The molecule initially contains high amounts of vibrational excitation in the methyl C–H stretch and the nearby benzene ring C–H stretch and it is in interaction with Ar. The two excited C–H stretches are coupled to each other through two C–C stretching, two H–C–C bending and one C–C–C bending modes, all of which are initially in the ground state. At 300 K, the energy lost by the excited molecule upon collision is not large and it increases slowly with increasing total vibrational energy content between 10 000 and 40 000 cm−1. Above the energy content of 40 000 cm−1, energy loss increases rapidly. Near 65 000 cm−1 energy loss takes a maximum value of about 1000 cm−1. The temperature dependence of energy loss is weak between 200 and 400 K. When the energy content is sufficiently high, either or both C–H bonds can dissociate, producing free radicals, C6H5CH2, C6H4CH3, ...

Classical trajectory study of the formation of XeH+ and XeCl+ in the Xe++HCl collision.

The collision-induced reaction of Xe+ with HCl has been studied by use of classical dynamics procedures at collision energies 2-20 eV using empirical potential parameters. The principal reaction pathway on the potential energy surface is the formation of XeH+ with the maximum reaction cross section, 1.2 A2, occurring at E=9 eV. At lower energies, the cross section for the charge transfer process Xe++HCl-->Xe+HCl+ is comparable to that for XeH+ formation, but at higher energies, it is larger by a factor of 2. The cross section of the XeCl+ formation is an order of magnitude smaller than that of XeH+. For both XeH+ and XeCl+ formations, the reaction threshold is approximately 2 eV. The XeH+ formation takes place immediately following the turning point in a direct-mode mechanism, whereas an indirect-mode mechanism operates in the formation of XeCl+. Both XeH+ and XeCl+ formations come mainly from the perpendicular configuration, Xe+...HCl, at the turning point. Product vibrational excitation is found to be strong in both XeH+ and XeCl+.

Vibrational relaxation of trapped molecules in solid matrices: OH(A Σ2+;v=1)/Ar

The vibrational relaxation of OH(A (2)Sigma(+);v=1) embedded in solid Ar has been studied over 4-80 K. The interaction model is based on OH undergoing local motions in a cage formed by a face-centered cubic stacking where the first shell atoms surround the guest and connect it to the heat bath through 12 ten-atom chains. The motions confined to the cage are the local translation and libration-rotation of OH and internal vibrations in OH...Ar, their energies being close to or a few times the energies of nearby first shell and chain atoms. The cage dynamics are studied by solving the equations of motion for the interaction between OH and first shell atoms, while energy propagation to the bulk phase through lattice chains is treated in the Langevin dynamics. Calculated energy transfer data are used in semiclassical procedure to obtain rate constants. In the early stage of interaction, OH transfers its energy to libration-rotation intramolecularily and then to the vibrations of the first shell and chain atoms on the time scale of several picoseconds. Libration-to-rotational transitions dispense the vibrational energy in small packages comparable to the lattice frequencies for ready flow. Energy propagation from the chains to the heat bath takes place on a long time scale of 10 ns or longer. Over the solid argon temperature range, the rate constant is on the order of 10(6) s(-1) and varies weakly with temperature.

Collision-induced dissociation of transition metal-oxide ions: Dynamics of VO + collision with Xe

The collision-induced dissociation of VO(+) by Xe has been studied by the use of classical dynamics procedures on London-Eyring-Polanyi-Sato potential-energy surfaces in the collision energy range of 5.0-30 eV. The dissociation threshold behavior and the dependence of reaction cross sections on the collision energy closely follow the observed data with the threshold energy of 6.00 eV. The principal reaction pathway is VO(+) + Xe --> V(+)+ O + Xe and the minor pathway is VO(+) + Xe--> VXe(+) + O. At higher collision energies (E > 8.0 eV), the former reaction preferentially occurs near the O-V(+)...Xe collinear and perpendicular alignments, but the latter only occurs near the perpendicular alignment. At lower energies close to the threshold, the reactions are found to occur near the collinear configuration. No reaction occurs in the collinear alignment V(+)-O...Xe. The high and low energy-transfer efficiencies of the collinear alignments O-V(+)...Xe and V(+)-O...Xe are attributed to the effects of mass distribution. The activation of the VO(+) bond toward the dissociation threshold occurs through a translation-to-vibration energy transfer in a strong collision on a time scale of about 50 fs.

Nd3+-Doped TiO2 Nanoparticles Prepared by Sol-Hydrothermal Process

Neodymium ion doped TiO 2 nanoparticles were prepared by sol-hydrothermal process using titanium isopropoxide as the TiO 2 precursor. The prepared neodymium ion doped TiO 2 nanoparticles were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM) and scanning electron microscopy (SEM). The photocatalytic degradation of 1,4-dichlorobenzene (DCB) was conducted in the suspension of Nd 3+ doped TiO 2 nanoparticles. The photocatalytic behaviors and microstructure of the prepared Nd 3+ -TiO 2 nanopowder were investigated as the function of dopant content. The effect of Nd 3+ content of the doped TiO 2 nanoparticles on the DCB photodegradation reaction rate was investigated and the first order reaction rate constant (k = 0.153min -1 ) for the doped nanoparticles was found to be significantly larger than that for the undoped TiO 2 nanoparticles. The result showed the optimum value of the Nd 3+ content to be 2 mole %.

Dependence of bond dissociation on initial vibrational phase in the He + I2 system

Abstract The dependence of the dissociation of an excited I2 in the HE + I2 system on initial vibrational phase has been explored using classical trajectory methods, with particular emphasis on those features of the trajectories responsible for the lower and upper limit of dissociative phase range. The presence of the regions of initial vibrational phase leading to dissociation and nondissociation is analyzed in detail. In the dissociative phase region, the lower limit is characterized by trajectories associated with a long dissociation time, while the upper limit represents an abrupt change in the vibrational energy transfer characteristics of I2.

Formation of Spherical and Rod-Shaped TiO2 Nanocrystals Prepared by Reverse Micelle Method

Uniform spherical- and rod-shaped TiO2 nanoparticles of anatase phase were prepared using decanoic acid at 300°C by reverse micelle method. The nanoparticles were characterized by transmission electron microscope (TEM), scanning electron microscope (SEM), X-ray diffractometry (XRD) and FT-Raman spectroscope. The content of decanoic acid and operating temperature were noted as crucial parameters, controlling the shape, size and phase of TiO2 nanoparticles. RMS roughness (1.62 nm), measured by atomic force microscope (AFM), confirmed its superiority over other methods. The DCB photodegradation reaction rate constant (first order) TiO2 nanoparticles was found superior to that of commercial TiO2, Degussa P-25.

Intramolecular energy flow and bond dissociation in iodoacetylene and iododiacetylene

Intermolecular and intramolecular energy flow and subsequent bond dissociation in collinear collisions I–C≡C–H+Ar and I–C≡C–C≡C–H+Ar have been studied by classical trajectory techniques over the collision energy range of 0 to 10 eV. When the molecule is initially in the ground state, the overall energy transfer in I–C≡C–H+Ar is very small, but in I–C≡C–C≡C–H+Ar it is large. The collisionally perturbed C–H bond stores a large amount of energy from translation for a brief period during the early stage of collision and transfers most of it to the inner region of the molecule, specifically to the low frequency C–I vibration. Thus the high‐frequency vibration of the perturbed C–H bond during the collision plays a crucial role in determining the extent of intramolecular energy transfer and, in turn, C–I dissociation. But in nondissociative collisions, there is another series of the C–H vibration at the latter stage of collision, transferring energy back to translation. This study also considers collision‐induce...