Vibrational Relaxation and Fragmentation in Icosahedral (Ar2+)Ar12 Clusters

Jongbaik Ree,김유항,Hyung Kyu Shin 대한화학회 2014 Bulletin of the Korean Chemical Society Vol.35 No.9

A dynamics study of relaxation and fragmentation of icosahedral argon cluster with a vibrationally excited Ar2 + (v) is presented. Local translation is shown to be responsible for inducing energy flow from the embedded ion to host atoms and fragmentation of the cluster consisting of various low frequency modes. The total potential energy of (Ar2 +)Ar12 is formulated using a building-up procedure of host-guest and host-host interactions. The time dependence of ion-to-host energy transfer is found to be tri-exponential, with the short-time process of ~100 ps contributing most to the overall relaxation process. Relaxation timescales are weakly dependent on both temperature (50-300 K) and initial vibrational excitation (v = 1-4). Nearly 27% of host atoms in the cluster with Ar2 + (v = 1) fragment immediately after energy flow, the extent increasing to ~43% for v = 4. The distribution of fragmentation products of (Ar2 +)Ar12 → (Ar2 +)Arn + (12-n)Ar are peaked around (Ar2 +)Ar8. The distribution of dissociation times reveals fragmentation from one hemisphere dominates that from the other. This effect is attributed to the initial fragmentation causing a sequential perturbation of adjacent atoms on the same icosahedral five-atom layer.

Theoretical Investigation of the Vibrational Relaxation of NO(${\upsilon}=1-7$) in Collisions with $O_{2}\;and\;N_{2}$

Jongbaik Ree Korean Chemical Society 1993 Bulletin of the Korean Chemical Society Vol.14 No.1

The vibrational relaxation rate constants of NO(v = 1-7) by $O_2\;and\;N_2$ have been calculated in the temperature range of 300-1000 K using the solution of the time-dependent Schrodinger equation. The calculated relaxation rate constants by $O_2$ increase monotonically with the vibrational energy level v, which is compatible with the experimental data, while those by $N_2$ are nearly independent of v in the range of $3.40 {\pm}1.60{\times}10_{-16} cm^3$/molecule-sec at 300 K. Those for NO(v) + $N_2$ are about 2-3 orders of magnitude smaller than those for NO(v) + $O_2$, because the latter is an exothermic processes while the former an endothermic. Relaxation processes can be interpreted by single-quantum V-V transition. The contributions of V-T/R transition and double-quantum V-V transition to the relaxation are negligible over the entire temperature range.

Energy Flow and Bond Dissociation of Vibrationally Excited Toluene in Collisions with N₂ and O₂

Ree, Jongbaik,Kim, Sung Hee,Lee, Sang Kwon Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.5

Energy flow and C-$H_{methyl}$ and C-$H_{ring}$ bond dissociations in vibrationally excited toluene in the collision with $N_2$ and $O_2$ have been studied by use of classical trajectory procedures. The energy lost by the vibrationally excited toluene upon collision is not large and it increases slowly with increasing total vibrational energy content between 5,000 and 45,000 $cm^{-1}$. Intermolecular energy transfer occurs via both of V-T and V-V transfers. Both of V-T and V-V transfers increase as the total vibrational energy of toluene increases. When the total energy content $E_T$ of toluene is sufficiently high, either C-H bond can dissociate. The C-$H_{methyl}$ dissociation probability is higher than the C-$H_{ring}$ dissociation probability, and that in the collision with $N_2$ is larger than with $O_2$.

Collision-induced Energy Transfer and Bond Dissociation in Toluene by H₂/D₂

Ree, Jongbaik,Kim, Yoo Hang,Shin, Hyung Kyu Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.12

Energy transfer and bond dissociation of $C-H_{methyl}$ and $C-H_{ring}$ in excited toluene in the collision with $H_2$ and $D_2$ have been studied by use of classical trajectory procedures at 300 K. Energy lost by the vibrationally excited toluene to the ground-state $H_2/D_2$ is not large, but the amount increases with increasing vibrational excitation from 5000 and $40,000cm^{-1}$. The principal energy transfer pathway is vibration to translation (V-T) in both systems. The vibration to vibration (V-V) step is important in toluene + $D_2$, but plays a minor role in toluene + $H_2$. When the incident molecule is also vibrationally excited, toluene loses energy to $D_2$, whereas it gains energy from $H_2$ instead. The overall extent of energy loss is greater in toluene + $D_2$ than that in toluene + $H_2$. The different efficiency of the energy transfer pathways in two collisions is mainly due to the near-resonant condition between $D_2$ and C-H vibrations. Collision-induced dissociation of $C-H_{methyl}$ and $C-H_{ring}$ bonds occurs when highly excited toluene ($55,000-70,400cm^{-1}$) interacts with the ground-state $H_2/D_2$. Dissociation probabilities are low ($10^{-5}{\sim}10^{-2}$) but increase exponentially with rising vibrational excitation. Intramolecular energy flow between the excited C-H bonds occurring on a subpicosecond timescale is responsible for the bond dissociation.

Vibrational Relaxation and Fragmentation in Icosahedral (Ar₂⁺)Ar₁₂ Clusters

Ree, Jongbaik,Kim, Yoo Hang,Shin, Hyung Kyu Korean Chemical Society 2014 Bulletin of the Korean Chemical Society Vol.35 No.9

A dynamics study of relaxation and fragmentation of icosahedral argon cluster with a vibrationally excited $Ar_2^+$ (${\nu}$) is presented. Local translation is shown to be responsible for inducing energy flow from the embedded ion to host atoms and fragmentation of the cluster consisting of various low frequency modes. The total potential energy of $(Ar_2^+)Ar_{12}$ is formulated using a building-up procedure of host-guest and host-host interactions. The time dependence of ion-to-host energy transfer is found to be tri-exponential, with the short-time process of ~100 ps contributing most to the overall relaxation process. Relaxation timescales are weakly dependent on both temperature (50-300 K) and initial vibrational excitation (${\nu}$ = 1-4). Nearly 27% of host atoms in the cluster with $Ar_2^+$ (${\nu}$ = 1) fragment immediately after energy flow, the extent increasing to ~43% for ${\nu}$ = 4. The distribution of fragmentation products of $(Ar_2^+)Ar_{12}{\rightarrow}(Ar_2^+)Ar_n+(12-n)Ar$ are peaked around $(Ar_2^+)Ar_8$. The distribution of dissociation times reveals fragmentation from one hemisphere dominates that from the other. This effect is attributed to the initial fragmentation causing a sequential perturbation of adjacent atoms on the same icosahedral five-atom layer.

Reaction Dynamics of CH₃ + HBr → CH₄ + Br at 150-1000 K

Ree, Jongbaik,Kim, Yoo Hang,Shin, Hyung Kyu Korean Chemical Society 2013 Bulletin of the Korean Chemical Society Vol.34 No.8

The kinetics of the radical-polar molecule reaction $CH_3+HBr{\rightarrow}CH_4+Br$ has been studied at temperatures between 150 and 1000 K using classical dynamics procedures. Potential energy surfaces constructed using analytical forms of inter- and intramolecular interaction energies show a shallow well and barrier in the entrance channel, which affect the collision dynamics at low temperatures. Different collision models are used to distinguish the reaction occurring at low- and high-temperature regions. The reaction proceeds rapidly via a complex-mode mechanism below room temperature showing strong negative temperature dependence, where the effects of molecular attraction, H-atom tunneling and recrossing of collision complexes are found to be important. The temperature dependence of the rate constant between 400 and 1000 K is positive, the values increasing in accordance with the increase of the mean speed of collision. The rate constant varies from $7.6{\times}10^{-12}$ at 150 K to $3.7{\times}10^{-12}$ at 1000 K via a minimum value of $2.5{\times}10^{-12}\;cm^3\;molecule^{-1}\;s^{-1}$ at 400 K.

과냉각 현상에 용액의 pH와 전해질이 미치는 영향

이종백(Ree, Jongbaik),김예린(Kim, Yae Rin),장소정(Chang, So Jeong),고경철(Ko, Kyoung Chul),이상권(Lee, Sang Kwon) 한국과학영재교육학회 2021 과학영재교육 Vol.13 No.1

이 연구는 광역시 소재 대학교 과학영재교육원 사사과정에서 진행하는 연구로 수행되었다. 물의 과냉각은 학생들 실험실에서 간단한 장치를 이용하여 쉽게 연구할 수 있다. 본 연구에서는 용액의 pH와 전해질이 물의 과냉각에 미치는 영향을 살펴보았다. 실험에서 온도 변화는 온도 센서와 MBL 장치를 이용하여 기록하였다. 또한 GAUSSIAN 프로그램을 이용하여 컴퓨터 시뮬레이션을 수행하고 실험 자료와 비교하였다. 물의 초기 온도가 높을수록 그리고 pH가 증가할수록 물의 과냉각이 더 잘 일어났다. pH가 낮을 때는 용액 중에 H3O+ 이온이 더 많이 존재하여 국소적으로 얼음 결정의 핵을 만들기가 더 쉽기 때문에 물의 과냉각이 잘 일어나지 않는다. 또한 시험관 내 물의 초기 온도가 80℃인 경우, pH가 7~13에서는 모든 물의 냉각 과정에서 물의 과냉각 현상이 나타나는 것을 알 수 있었다. 전해질이 첨가된 용액에는 전해질이 없는 경우에 비해 물의 과냉각이 훨씬 덜 일어나는 것을 알 수 있었다. 따라서 냉각 곡선에서 물의 과냉각 현상은 물이 국소적으로 결정핵을 더 쉽게 형성할 수 있는 환경과 관련이 있다는 것을 알 수 있다; 만일 결정핵을 쉽게 형성할 수 있다면 국소적으로 형성된 얼음 결정에 의해 물은 과냉각 없이 전체적으로 얼게 된다. 반면에 결정핵이 쉽게 형성될 수 없다면 결정핵의 형성은 지연되고 따라서 물은 과냉각된다. 컴퓨터 시뮬레이션 결과, H3O+ 이온에 의해 수소 결합의 형성이 더 촉진될 수 있다는 것이 예측되었다. This study is based on Research and Education (R&E) project in the University located in metropolitan city. Supercooling of water can be easily studied with a simple apparatus suitable for the student laboratory. We investigated the effects of the pH and electrolyte of the solution on the occurrence of supercooling of water. The temperature variations in the experiment were recorded using temperature sensor and MBL apparatus in the cooling the solution. The computer simulations were carried out using GAUSSIAN program and compared with the experimental data. As the initial temperature and pH of a solution become higher, supercooling of water occurs more easily. When the pH of a solution is low, supercooling of water does not occur easily because the presence of H3O+ ion accelerates the formation of ice crystals locally. Further, when the initial temperature of a solution is 80℃, supercooling of water occurs at all cooling experiments if the pH of a solution is between 7 to 13. When electrolytes are added in the solution, the occurrence of supercooling of water is not easy compared to the case of the absence of electrolytes. Therefore, we correlate the occurrence of supercooling of water with the circumstance of the solution to nucleate ice more easily; if it nucleates easily, the layer of ice crystals formed locally will initiate freezing of the bulk water without supercooling. On the other hand, If the circumstance is unable to nucleate ice easily, ice nucleation is delayed and the water is supercooled. As the result of the computer simulation, it is expected that the formation of the hydrogen bond can be accelerated by the presence of H3O+ ion.

정부출연연의 대리문제와 PBS의 한계

길종백(Kil Jongbaik),정병걸(Jung Byung Kul),염재호(Yeon Jaeho) 한국조직학회 2009 한국조직학회보 Vol.6 No.2

지역 국립대학 행정조직의 실태와 개선방안: 교직원 인식조사를 중심으로

길종백 ( Gil Jongbaik ),하정봉 ( Ha Jung-bong ) 한국거버넌스학회 2016 한국거버넌스학회보 Vol.23 No.3

학령인구 감소와 대학구조조정이라는 대학을 둘러싼 환경변화에 대응하기 위해서는 대학경쟁력의 한축인 행정조직의 효율성을 제고하는 것도 중요한 과제라고 할 수 있다. 이러한 문제의식에서 본 논문은 지역중심 국립대학 행정조직에 대한 연구가 많지 않은 가운데 S대학 교직원을 대상으로 한 설문조사를 통해 대학행정 조직의 전반적인 운영실태를 분석하고 개선방안을 제시하였다. 실태분석 결과 대학 행정조직은 획일적인 편제하에서 직원들의 재량이 제약되어 있는 편이었다. 그리고 성과평가제 등의 신공공관리적 요소가 일부 도입되고 있으나 이러한 제도에 대한 만족 수준은 낮은 것으로 조사되었다. 이에 대해 본 연구는 대학행정조직 효율성 제고를 위한 개선방안으로 첫째 본부 및 단과대 행정조직의 재구조화, 둘째 행정실 최소화 등 행정조직의 개편, 셋째 내부사업가제도 등의 확대와 실질적 인센티브 부여, 넷째 성과평가제정착을 위한 외부평가 확대 및 대학 비전·미션의 명확화, 다섯째 성과평가와 역량제고 프로그램의 연계강화 및 직원 파견연수 활성화 등을 제시하였다. In order to cope with restructuring of universities by a government and continuous declining of university enrollments, it has emerged as an important task to improve the efficiency of administrative organization. However, researches on administrative organization of region-centered national university in Korea have not much attempted. This study examined the behavior and perception of S university administrative staff on organizational management mainly by survey analysis. The results of examination indicate that the discretion of staff is somewhat constrained with monolithic organization. The New Public Administrative factors such as performance evaluation system have been partly introduced but a satisfaction level for these systems was low. Therefore, this study suggested practical ways for improving organizational efficiency such as the empowerment of self-organizing ability to the university, restructuring of administrative organization, promotion of internal entrepreneurship system, shaping common vision and mission for the effective performance evaluation system, strengthening the linkage between capability power-up program and performance evaluation.

Reaction between Gas-phase Hydrogen Atom and Chemisorbed Bromine Atoms on a Silicon(001)-(2?1) Surface

Jongkeun Park,Jongbaik Ree*,Sang Kwon Lee,김유항 대한화학회 2007 Bulletin of the Korean Chemical Society Vol.28 No.12

The reaction between gas-phase atomic hydrogen and highly covered chemisorbed bromine atoms on a silicon(001)-(21) surface is studied by use of the classical trajectory approach. The model is based on reaction zone consisting of H, Br and Si atom interacting with a finite number of primary system silicon atoms, which are coupled to the heat bath. The calculations were carried out in the temperature range 300-2500 K for the gaseous H atom and 0-700 K for the surface, respectively. All reactive events occur in a single impact collision on a subpicosecond scale, following the Eley-Rideal mechanism. The reaction probability is dependent upon the gas temperature and the largest near 800 K, but it is essentially independent of the surface temperature. The reaction energy available for the product state is small, and most of the reaction exothermicity deposits in vibration and translation of the product, HBr molecule.