• Bulletin of the Korean Chemical Society
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• v.31 no.3
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• pp.595-598
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• 2010

Ab initio and DFT molecular orbital calculations predict that acetyl radical reacts with acetylene through interactions primarily involving the SOMO of the radical and the in-plane ${\pi}$-bond of acetylene. An energy barrier (${\Delta}E_1$) of 39.6 kJ $mol^{-1}$ is predicted for the preferred anti arrangement of reactants at the CCSD(T)/cc-pVDZ//BHandHLYP/cc-pVDZ level of theory. NBO analysis reveals additional interactions between the radical SOMO and the nearby C-H ${\sigma}$-bond in acetylene worth about 10% of the total transition state interaction energy. This type of orbital interaction has not previously been observed in radical addition reactions involving C-C ${\pi}$-bonds.

• Journal of Powder Materials
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• v.9 no.3
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• pp.148-152
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• 2002

The microstructures and indentation fracture of pressureless-sintered $DyNbO_4$ crystalline were investigated as a basic study for the application of weak phase of fibrous monolithic composites. They were comprised with many lamella twins as well as micro-cracks at the grain boundaries. The hardness at room temperature was remarkably low value(575 Hv) due to the low relative density and existence of microcracks at grain boundaries. The main fracture mode was a typical intergranular fracture, and showed remarkable micro-cracking effect. The heavy plastic deformation was observed around the site of indentation. In addition, the $DyNbO_4$ was expected to apply as a weak phase in the fibrous monolithic composites because of the low hardness and easily plastic deformation that could be led the preferable pulled-out and microcracking toughening under the failure.

• Bulletin of the Korean Chemical Society
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• v.34 no.12
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• pp.3591-3596
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• 2013

The enantioselective aza-Morita Baylis Hillman reaction of nitroalkene and N-tosylimine catalyzed by thiourea-tertiary amine has been investigated using density functional theory. Enantioselectivity is dominated by the cooperative effect of non-covalent and weak covalent interactions imposed by different units of catalyst. As Lewis base, the tertiary amine unit activates nitroalkene via weak covalent bond. The weak covalent interaction orients the reaction in a major path with smaller variations of this bond. The aromatic ring unit activates N-tosylimine via ${\pi}-{\pi}$ stacking. The non-covalent interaction selects the major path with smaller changes of the efficient packing areas. Thiourea unit donates more compact H-bonded network for species of the major path. The calculated ee value in xylene solution phase (97.6%) is much higher than that in N,N-Dimethylformamide (27.2%). Our conclusion is also supported by NBO analysis.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2003.11a
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• pp.186-190
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• 2003

유리고화체의 내구성과 조성에 관한 이 연구의 목적은 구조적 모델, 비가교 산소 모델(NBO) 및 간단한 경험적 모델(Valence-oxygen)과 함에 침출실험결과들을 비교하는 것이다. 조성에 기초한 모델들 사이의 연관성들은 이와 같은 모델들이 지질학적 유리와 제조된 유리의 관련성에 대해 유리고화체의 내구성을 설명할 수 있다는 것을 나타낸다 이러한 관계는 유리고화체의 장기간 내구성을 결정하는데 도움을 줄 수 있으며, 모델을 통한 유리고화체의 조성에 의한 실험결과에의 영향성을 검토하였다 9$0^{\circ}C$에서 7일간 수행된 PCT 침출시험을 대상으로 모델들을 비교하였으며 Ash Loading wt%가 증가할수록 망목형성이온이 증가하기 때문에 침출농도 및 침출분율이 감소하는 것을 확인 할 수 있었으며, VO model의 변수 값이 증가할수록 주요 유리매질의 침출분율은 완만한 기울기를 가지며 감소하다. 금속류의 침출분율은 VO model의 변수 값이 감소함에 따라 대체적으로 증가함을 확인 할 수 있었다.

• Journal of the Korean Institute of Telematics and Electronics
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• v.24 no.3
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• pp.510-516
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• 1987

An analysis and numerical computations relating to the coupling of optical modes between two neighboring waveguides are discussed. The waveguides are fabricated with Lithium Niobate as guide 1 and Vanadium Oxide as guide 2. In a wave guide system that incorporates two lossless guides, a complete transfer of power from one guide to another can occur when the waveguides are (1) identical or (2) the modes in each guide have identical phase constants. Here we discuss the coupling effects when the guides are dissimilar with respect to both geometry and losses. In thers results, we show that power transfer can occur between the two guides, one lossy and the other lossless, provided the phase matched condition is satisfied. When properly coupled, the power attenuation varies according to the amount of coupling.

• Journal of the Korean Ceramic Society
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• v.37 no.9
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• pp.900-908
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• 2000

일반적인 유리용융과 열처리법을 이용하여 많은 양의 금속구리 미립자가 분산된 Zinc Phosphate 유리를 제조하였다. 금속산화물로는 Cu$_2$O를, 환원제로는 SnO를 사용하였다. XRD와 전자회절로부터 열처리에 의해 금속구리의 결정상이 석출됨을 알 수 있었고, TEM에 의해 석출상의 크기는 수~20nm 정도임을 알 수 있었다. 또한 570nm에서의 광흡수 피크로부터도 금속구리의 석출을 확인할 수 있었다. 석출입자의 크기와 흡광은 석출을 위한 열처리 온도와 시간이 증가함에 따라 증가하였다. XPS 스펙트럼으로는 구리의 산화상태 중 Cu$^{2+}$ 이온의 상태만을 분명히 할 수 있었다. 매질유리의 BO/NBO의 비는 열처리 전후 크게 변화가 없었으며, 열처리 후 Cu$^{2+}$ 이온이 다소 감소되는 경향을 보였다.

• Bulletin of the Korean Chemical Society
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• v.34 no.11
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• pp.3274-3278
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• 2013

$CF_2Cl{\cdots}Cl$, an elusive photo-isomer of $CF_2Cl_2$, has been observed in matrix IR spectra from the precursors exposed to radiation from laser ablation of transition-metals. Other plausible products, $CFCl_2{\cdots}F$ and $FClC{\cdots}F-Cl$ are not detected due to their considerably higher energies. Parallel to its previously reported analogues, the C-X bonds are considerably stronger than those of the reactant, and particularly the Cl atom that is weakly bound to the residual Cl atom forms an unusually strong carbon-halogen bond. NBO analysis reveals that the C-Cl bond is a true double bond, and the weak $Cl{\cdots}Cl$ bond is largely ionic, $F_2C=Cl^{\delta+}{\cdots}Cl^{\delta-}$. IRC computation reproduces smooth inter-conversion between the reactant and product, and the transition state is energetically close to the product, consistent with its prompt disappearance in the early stage of photolysis.

• Bulletin of the Korean Chemical Society
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• v.31 no.4
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• pp.941-948
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• 2010

Ab initio and density functional theory methods have been employed to study all theoretically possible conformers of fluoroacetic acid. Molecular geometries and energetic of cis and trans monomers and cis dimers in gaseous phase have been obtained using HF, B3LYP and MP2 levels of theory, implementing 6-311++G(d,p) basis set. It was found that cis rotamers are more stable. In addition, it was found that in comparison with acetic acid the strength of hydrogen bonding in fluoroacetic acid decreased. The infrared spectrum frequencies and the vibrational frequency shifts are reported. Natural population and atom in molecule analysis performed to predict electrostatic interactions in the cyclic H-bonded complexes and charges. The proton transfer reaction is studied and activation energy is compared with acetic acid proton transfer reaction.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.91-92
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• 2021

In the present work, we simulated and explained the bonding of three alkanethiols - hexanethiol (HT), decanethiol (DT), and 11-mercaptoundecanoic acid (MDA) - with Fe(110) surface and Fe2 clusters using Density Functional Theory (DFT) to probe the corrosion inhibition mechanisms. The interaction energies computed from periodic DFT calculations successfully predicted the experimental inhibition performance. We have found strong covalent bond formation between S(thiol) and Fe-atoms in both approaches, further confirmed by the projected density of states and electron density difference. Besides, natural bond orbital (NBO) charge distribution showed that DT had stronger electron-donation and back-donation synergic interactions with Fe-atoms.

• Korean Journal of Crystallography
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• v.4 no.2
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• pp.74-85
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• 1993

Single crystals of LiNbO3 have found extensive application in electro-optic and nonlinear optic devices. However, laser-induced refartive index inhomogeneities, which have been labeled opical damage impose limits on device optical damage in LiNbO3 is imporved if more than 4.5 rml% MgO is added to the melt The laser damage thrueshold increased as much as 100 times better then that of undoped crystals. The MgO doped cystal has thus been urterlsiv81y studied since then. In the study, Mgo:LiNbOs(MLA) single crystals dopsd with 0, 2.5, 5.0, 7.5, 10.0 mol% MgO have been grown by the czocrualski technique. The metls were prepared in the platinum crluible and 15∼20mm diameter crystals were grown with a length of 20∼30mm in a resitance heater. The growth rate was 2.5mm/hr, the rotation speed 15rpn. Before sawing MLN single crystals were annealed for 24 hours under atmosphere at a temperature of 1080℃. After sawing, we have found an annual ring cross section of MNA crystals only in the direction of perpendicilar to the c-axis. Nonuniform dispusion of MgO was pointed out that the cuties of the state of oxide were strongly affected by oxygen partial pressure in.