• Bulletin of the Korean Chemical Society
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• 제19권9호
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• pp.980-985
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• 1998

The excited-state intramolecular proton transfer (ESIPT) emission has been observed for 0.01 mM p-aminosalicylic acid (AS) in nonpolar aprotic solvents as demonstrated by the large Stokes' shifted fluorescence emission around 440 nm in addition to the normal emission at 330 nm. However in aprotic polar solvent such as acetonitrile, the large Stokes' shifted emission band becomes broadened, indicating existence of another emission band originated from intramolecular charge transfer (ICT). It is noteworthy that in protic solvents such as methanol and ethanol the normal and ICT emissions are quenched as the AS concentration decreases, followed by the appearance of new emission at 380 nm. These results are interpreted in terms of ESIPT coupled charge transfer in AS. Being consistent with these steady-state spectroscopic results, the picosecond time-resolved fluorescence study unravelled the decay dynamics of the ESIPT and ICT state ca. 300 ps and ca. 150 ps, respectively with ca. 40 ps for the relaxation time to form the ICT state.

• 대한화학회지
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• 제55권3호
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• pp.385-391
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• 2011

Phenol-$(H_2O)_2$ 착물의 여기상태 수소 결합 동력학을 시간 의존 밀도 함수 이론(TDDFT) 법으로 연구하였다. 수소-결합된 착물에 대한 바닥 상태 및 다른 전자 여기 상태들 ($S_1$와 $T_1$)에서의 기하학적 구조와 IR 스펙트라를 밀도 함수 이론(DFT)와 TDDFT 방법을 사용하여 계산하였다. 페놀과 두 물분자 간에 3개의 수소 결합으로 구성된 고리가 형성되었다. 세 개의 수소 결합에서 분자간 수소결합 $O_1-H_2{\cdots}O_3-H$은 $S_1$ 그리고 $T_1$ 상태에서 더 강해졌지만, 수소결합 $O_5-H_6{\cdots}O_1-H$은 $S_1$과 $T_1$상태에서 약해졌다. 이러한 결과들은 다른 전자 상태에서 수소 결합과 hydrogen-bonding groups의 결합 길이의 변화를 이론적으로 모니터링하여 얻었다. 수소 결합 $O_1-H_2{\cdots}O_3-H$가 $S_1$와 $T_1$ 상태 모두에서 강화된다는 것은 OH(phenol)의 계산된 신축 진동 모드가 광 여기에 의해 적색-이동한다는 것으로부터 확인 되었다. 전자 여기 상태에서 수소 결합이 강해지고 약해지는 행동은 phenol-$(H_2O)_n$의 다른 고리 구조에 존재할 수 있다.

• Structural Engineering and Mechanics
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• 제33권1호
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• pp.47-66
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• 2009

Radiation damping due to wave propagation in unbounded domains may cause a significant reduction of structural vibrations when excited near resonance. Here a novel matrix-valued algebraic Pad$\acute{e}$-like stiffness formulation in the frequency-domain and a corresponding state equation in the time domain are elaborated for a soil-structure interaction problem with a layered soil excited in a transient manner by a flexible rotor during startup and shutdown. The contribution of radiation damping caused by a soil-layer upon a rigid bedrock is characterized by the corresponding amount of critical damping as it is used in structural dynamics.

• Journal of Photoscience
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• 제6권3호
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• pp.123-128
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• 1999

Dynamics of many ultrafast processes are markedly slowed down in various organized molecular assemblies compared to ordinary liquids. We will show that the solvation dynamics of water molecules is affected amost dramatically and is retarded by 3 ∼4 orders of magnitude in microemulsions, micells and lipids. We will also discuss how the access to fewer water molucules and the drastically altered local pH in an organized asembly affected the excited state proton transfer processes. Finally, we will show how surface second haromonic generation can be used to study the air-water surface.

• Bulletin of the Korean Chemical Society
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• 제33권11호
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• pp.3618-3624
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• 2012

Photodissociation dynamics of propiolic acid ($HC{\equiv}C-COOH$) at 212 nm in the gas phase was investigated by measuring rotationally resolved laser-induced fluorescence spectra of OH ($^2{\Pi}$) radicals exclusively produced in the ground electronic state. From the spectra, internal energies of OH and total translational energy of products were determined. The electronic transition at 212 nm responsible for OH dissociation was assigned as the ${\pi}_{C{\equiv}C}{\rightarrow}{\pi}^*{_{C=O}}$ transition by time-dependent density functional theory calculations. Potential energy surfaces of both the ground and electronically excited states were obtained employing quantum chemical calculations. It was suggested that the dissociation of OH from propiolic acid excited at 212 nm should take place along the $S_1/T_1$ potential energy surfaces after internal conversion and/or intersystem crossing from the initially populated $S_2$ state based upon the potential energy calculations and model calculations for energy partitioning of the available energy among products.

• Bulletin of the Korean Chemical Society
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• 제25권8호
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• pp.1130-1132
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• 2004

Photodissociation dynamics of tert-butyl isocyanide at 193 nm has been investigated by measuring rotationally resolved laser induced fluorescence spectra of CN fragments that were exclusively produced in the ground electronic state. From the spectra, internal energies of CN and translational energy releases in the products were obtained. The dissociation takes place in the excited triplet states which are strongly repulsive along the dissociation coordinate via curve crossing from the initially prepared state.

• Bulletin of the Korean Chemical Society
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• 제16권3호
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• pp.256-260
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• 1995

Laser induced fluorescence spectra of OH produced from photodissociation of $H_2O_2$ at 280-290 nm in the gas phase have been observed. By analyzing the Doppler profiles, the anisotropy parameter($\beta$ =-0.7) and the center of mass translational energy of the fragments have been measured. The measured energy distribution is well described by an impulsive model. The excited state leading to dissociation is found to be of 1Au symmetry. The dissociation from this state is prompt and direct with the fragment OH rotating in the plane perpendicular to the O-O bond axis.

• Bulletin of the Korean Chemical Society
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• 제18권12호
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• pp.1274-1280
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• 1997

The photodissociation dynamics of CH2I2 has been studied at 304 nm by state-selective photofragment translational spectroscopy. Velocity distributions, anisotropy parameters, and relative quantum yields are obtained for the ground I(2P3/2) and spin-orbit excited state I*(2P1/2) iodine atoms, which are produced from photodissociation of CH2I2 at this wavelength. These processes are found to occur via B1 ← A1 type electronic transitions. The quantum yield of I*(2P1/2) is determined to be 0.25, indicating that the formation of ground state iodine is clearly the favored dissociation channel in the 304 nm wavelength region. From the angular distribution of dissociation products, the anisotropy parameters are determined to be β(I)=0.4 for the I(2P3/2) and β(I*)=0.55 for the I*(2P1/2) which substantially differ from the limiting value of 1.13. The positive values of anisotropy parameter, however, show that the primary processes for I and I* formation channels proceed dominantly via a transition which is parallel to I-I axis. The above results are interpreted in terms of dual path formation of iodine atoms from two different excited states, i.e., a direct and an indirect dissociation via curve crossing between these states. The translational energy distributions of recoil fragments reveal that a large fraction of the available energy goes into the internal excitation of the CH2I photofragment; < Eint > /Eavl=0.80 and 0.82 for the I and I* formation channels, respectively. The quantitative analysis for the energy partitioning of available energy into the photofragments is used to compare the experimental results with the prediction of direct impulsive model for photodissociation dynamics.

• 한국광과학회:학술대회논문집
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• 한국광과학회 1999년도 학술대회지
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• pp.84-84
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• 1999

• 대한전기학회:학술대회논문집
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• 대한전기학회 2002년도 추계학술대회 논문집 전력기술부문
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• pp.85-87
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• 2002

The paper describes the formulation of state matrix equations from the linearized multi-machine power system including network dynamics and the application of IEEE First Benchmark Model. The eigenvalues of IEEE First Benchmark Model are investigated not only by changing the compensation of series capacitance at no-load conditions, but also by varying the generator loading at fixed compensation of capacitance. In addition, the pure electrical self-excited mode is also examined by an eigen analysis and time domain simulation.