So-Yeon Kim, Jeongmook Lee, and Sang Kyu Kim, Young S. Choi


"Nonplanar structure of C6H5SCF3 facilitates πσ*-mediated
photodissociation reaction on the S1 state

Chemical Physics Letters, 659, 43-47 (2016)

    Vibrational structure of trifluoromethylthiobenzene (C6H5SCF3) on the S1 state has been investigated by resonance-enhanced two-photon ionization spectroscopy and nature of predissociation dynamics is inferred from homogeneously broadened spectral features. As (C6H5SCF3) adopts a nonplanar structure in both the S0 and S1 states, the effective adiabatic barrier generated by avoided crossing of opticallybright bound S1 (ππ*) and dark-repulsive S2 (πσ*) surfaces along the reaction coordinate is significantly lowered, giving the S1 lifetime of ~300 fs. This experiment demonstrates that the molecular structure spanned by the reactive flux near the curve-crossing region dictates reaction rate as well as nonadiabatic transition probability.



   So-Yeon Kim, Jeongmook Lee, and Sang Kyu Kim


"H/D Substitution Makes Difference in Photochemical Studies:
the Case of Dimethylamine

Rapid Communication in Photoscience, 4, 3, 63-66 (2015)

    When the molecule in the excited state is subject to prompt predissociation, it is quite nontrivial to obtain vibrational structure of the excited state in general. This applies to the case of photochemistry of dimethylamine (DMA:(CH3)2NH). When DMA is excited to its first electronically excited state (S1), the N-H bond dissociation occurs promptly. Therefore, S1 vibronic bands are homogeneously broadened to give extremely small ionization cross sections and heavily-congested spectral features, making infeasible any reasonable spectral assignment. Here, we demonstrate that the predissociation rate of the excited state could be significantly reduced by the NH/ND substitution to give the much better-resolved S1 spectral feature, revealing the vibrational structure of the excited state of DMA-d1 ((CH3)2ND) for the first time.



   Hyun Sik You, Songhee Han, Jun-Ho Yoon, Jeong Sik Lim, Jeongmook Lee,
So-Yeon Kim, Doo-Sik Ahn, Jean Sun Lim, and Sang Kyu Kim


"Structure and Dynamic Role of Conical Intersections
in the πσ*-mediated Photodissociation Reactions

International Reviews in Physical Chemistry, 34, 3, 429-459 (2015)

    Conical intersection as a dynamic funnel in nonadiabatic transition dictates many important chemical reaction outputs such as reaction rates, yields, and energy disposals especially for chemical reactions taking place on electronically excited states. Therefore, the energetics and topology of conical intersections have been subjected to intensive theoretical and experimental studies for decades as these things are the keys to understanding and controlling nonadiabatic transitions which are ubiquitous in nature. In this article, we focus on πσ*-mediated photodissociation reactions of thiophenols and thioanisoles. Interestingly, for these chemical systems, the nonadiabatic transition probability can be precisely measured as a function of the excitation energy, giving a great opportunity for spectroscopic characterization of the multi-dimensional conical intersection seam that governs the nonadiabatic transition dynamics of polyatomic molecules. The passage of the reactive flux in the proximity of the conical intersection gives rise to dynamic resonances corresponding to dramatic state-specific increases of the nonadiabatic transition probability. Accordingly, it is found that the electronic and nuclear configurations of the reactive flux and their evolution, coupled to the conical intersection seam, are critical in nonadiabatic transition dynamics. Nonadiabaticity is found to be extremely sensitive to the conformational molecular structure, and this has been demonstrated in the photodissociation dynamics of the chemical derivatives of thiophenol. Intramolecular vibrational redistribution, which is nontrivial in surmounting the reaction barrier, is found to wash out state-specific dynamic resonances, implying the importance of the dynamic interplay between vibrational energy flow and nonadiabatic transition. The experimental results on conical intersection dynamics presented in this review provide many interesting and important issues to be pursued in the near future by both theoreticians and experimentalists.



   Hyun Sik You, Songhee Han, Jean Sun Lim, and Sang Kyu Kim


"(*/*) Conical Intersection Seam Experimentally Observed
in the S–D Bond Dissociation Reaction of Thiophenol-d1

J. Phys. Chem. Lett., 6, 3202-3208 (2015)

    Surface crossing of bound (S1, *) and continuum (S2, *) states has been observed in the ultrafast S–D bond dissociation reaction of thiophenol-d1. It is manifested by an unanticipated variation of fragment angular distribution as a function of the excitation energy. The anisotropy parameter () of +0.25 at the S1 origin decreases to -0.60 at 600 cm–1 above the S1 zero-point level, giving a broad peak in with a bandwidth of 200 cm–1. The peak in is ascribed to the in-plane S-D bending mode excitation by which the nuclear configuration in the proximity of the S1/S2 conical intersection seam is directly accessed, showing a mixed character of parallel (S1–S0) and perpendicular (S2–S0) transition dipole moments at the same time. As a result, the dynamic aspect of the conical intersection is experimentally revealed here through direct access to the nuclear configuration on the multidimensional conical intersection seam.



   Songhee Han, Hyun Sik You, So-Yeon Kim, and Sang Kyu Kim


"Dynamic Role of the Intramolecular Hydrogen Bonding in Nonadiabatic Chemistry
Revealed in the UV Photodissociation Reactions of 2-Fluorothiophenol and 2-Chlorothiophenol

J. Phys. Chem. A, 118, 6940-6949 (2014)

    The dynamic interplay between the intramolecular hydrogen bonding and intramolecular vibrational redistribution is found to be critical in nonadiabatic reaction dynamics. Herein, it has been demonstrated that the molecular planarity, directed by the intramolecular hydrogen bonding, plays an important role in the nonadiabatic passage of the reactive flux at the conical intersection in the photodissociation reactions of 2-fluorothiophenol and 2-chlorothiophenol. As the internal energy increases in the excited state, the intramolecular hydrogen bonding of 2-fluorothiophenol loosens. The floppiness brought into the molecular structure then modifies the dynamic path of the reactive flux, leading to the diminishment of the nonadiabatic transition probability at the conical intersection. On the contrary, for 2-chlorothiophenol having the relatively stronger intramolecular hydrogen bonding, the reactive flux seems to retain the molecular planarity even with the increase of the internal energy as manifested by the constant nonadiabatic transition probability over the wide range of the S1 internal energy. The effect of the intramolecular hydrogen bonding on the molecular structure and its relation to the nonadiabatic dynamics along the tunneling path has been experimentally demonstrated.  



   Dahyi Jeong, Ki Young Yeon, and Sang Kyu Kim


"Tip-enhanced Electron Emission Microscopy Coupled with the Femtosecond Laser Pulse"

Bull. Korean Chem. Soc., 35, 891 (2014)

    The ultrashort electron pulse, laser-emitted from the metal tip apex has been characterized and used as a probing source for a new electron microscope to visualize the morphology of the gold-mesh in the nanometric resolution. As the gap between the tungsten tip and Au-surface is approached within a few nm, the large electromagnetic field enhancement for the incident P-polarized laser pulse with respect to the tip-sample axis is strongly observed. Here, we demonstrate that the time-resolved tip-enhanced electron emission microscope (TEEM) can be implemented on the laboratory table top to give the two-dimensional image, opening lots of challenges and opportunities in the near future.  



   Jun-Ho Yoon, Kyung Chul Woo, and Sang Kyu Kim


"Vibronic Structures and Dynamics of the Predissociating Dimethyl Sulfide
and its Isotopomers (CH3SCH3, CD3SCD3, CH3SCD3) at the Conical Intersection"

Phys. Chem. Chem. Phys., 16, 8949-8955 (2014)

    Conical intersection seam comprised of crossing surfaces of two lowest excited states of dimethyl sulfide (DMS) has been directly accessed by the one-photon excitation from the ground equilibrium state. Since the S-C bond rupture takes place promptly, the molecular structure on the excited state effectively belongs to CS symmetry. Namely, excited states of 11B1 and 11A2 in C2V become 11A and 21A states in CS, respectively, and the optical transition from the ground equilibrium state to the dissociating molecule at the conical intersection seam is symmetry-allowed to facilitate the nonadiabatic transition on the 21A state, leading eventually to the CH3S + CH3 products. The dynamic study of DMS, in this sense, gives the great opportunity to unravel the vibronic structure of the conical intersection seam by the conventional one-photon excitation method. In this work, utilizing the photofragment excitation (PHOFEX) spectroscopic method, the vibronic structures of DMS and its isotope analogs (CD3SCD3, CH3SCD3) at the conical intersection seam have been revealed, providing accurate lifetimes and detailed dynamics associated with individual vibronic transitions. Lifetime of the excited DMS is estimated to be ~ 100 fs, indicating that the dissociation is complete within one single oscillation in the conical intersection region. It is also found that the symmetric CSC stretching mode is strongly coupled to the reaction coordinate, as manifested by our experimental finding that the fragmentation yield of the S-CD3 bond is enhanced compared to that of the S-CH3 bond in the CH3SCD3 dissociation reaction only when the CSC symmetric stretching vibrational mode is excited at the conical intersection region. This work demonstrates that the better understanding of the excited state could make the bond-selective chemistry into reality.  



   Jeongmook Lee, So-Yeon Kim, and Sang Kyu Kim


"Spectroscopic Separation of the Methyl Internal Rotational Isomers
of Thioanisole Isotopomers (C6H5S-CH2D and C6H5S-CHD2)"

J. Phys. Chem. A, 118, 1850 (2014)

    Two distinct rotational isomers of thioanisole-d1 (C6H5S-CH2D) and thioanisole-d2 (C6H5S-CHD2) with respect to the internal rotation of the methyl moiety have been identified and characterized spectroscopically using the resonantly-enhanced two photon ionization (R2PI), UV-UV hole burning, and slow-electron velocity map imaging (SEVI) techniques. From the statistical weights, the definite assignment for the specific rotational isomer of each isotopomer has been successfully done, providing isomer-specific ionization energies and vibrational frequencies of S1/D0 states. Detailed molecular structures, the methyl internal-rotor barrier, and normal mode descriptions for selective vibrations are discussed with the aid of density functional theory calculations.



   Songhee Han, Jeong Sik Lim, Jun-Ho Yoon, Jeongmook Lee, So-Yeon Kim,
 and Sang Kyu Kim


"Conical Intersection Seam and Bound Resonances Embedded in Continuum
Observed in the Photodissociation of Thioanisole-d3"

J. Chem. Phys., 140, 054307 (2014)

    Herein, the multi-dimensional nature of the conical intersection seam has been experimentally revealed in the photodissociation reaction of thioanisole-d3 (C6H5SCD3) excited on S1, giving C6H5S· ( or math) + ·CD3 products. The translational energy distribution of the nascent ·CD3 fragment, reflecting the relative yields of the C6H5S· () and C6H5S· (math) products, was measured at each S1 vibronic band using the velocity map ion imaging technique. Direct access of the reactant flux to the conical intersection seam leads to the increase of the nonadiabatic transition probability resulting in sharp resonances in the math/ C6H5S· product branching ratio at several distinct S1 vibronic bands. The nature of the S1 vibronic bands associated with such dynamic resonances was clarified by the mass-analyzed threshold ionization spectroscopy. The bound state embedded in continuum generated by the conical intersection is observed as a distinct dynamic resonance, revealing the nature of the nuclear motion responsible for the nonadiabatic coupling of two potential energy surfaces at the conical intersection. The multi-dimensional facets of the conical intersection seam in terms of its detailed structure and dynamic role are discussed with the aid of theoretical calculations. 



   Jeongmook Lee, So-Yeon Kim, and Sang Kyu Kim


"Spectroscopic Study on Nonradiative Transition and Ionization of
5-methylpyrimidine at S
1 Probed by the Slow-electron Velocity-map Imaging (SEVI) Technique"

Chem. Phys. Lett., 568, 36 (2013)

    Slow electron velocity-map imaging (SEVI) has been employed for the ionization spectroscopic study of the jet-cooled 5-methylpyrimidine in the first singlet 1(n*) excited state. Resonant-enhanced two-color two-photon (1+1) ionization spectrum gives well-resolved S1 vibrational structures up to ~ 2400 cm-1 above the origin whereas spectral bands becomes completely broadened in the higher energy region as coupling of individual S1 bands to dark states becomes significant. Ionization of the S1 5-methylpyrimidine with different ionization wavelengths at several different delay times reveals the property of low-lying 3(*) triplet dark state which is prepared by fast nonadiabatic transition. SEVI spectra taken via various S1 intermediate states provide the detailed vibrational structures of the 5-methylpyrimidine cation (D0), also giving the adiabatic ionization energy of 9.1052 ± 0.0030 eV (73 438 ± 24 cm-1). Geometrical changes in the S0-S1-D0 transitions are discussed from Franck-Condon simulations based on calculations by (time-dependent) density functional theory.



   Jeongmook Lee, Doo-Sik Ahn, and Sang Kyu Kim


"Valence Electron Ionization Dynamics of Chromium by a Photoelectron Imaging Technique: 
J+ -Dependent State and Angular Distribution

J. Phys. Chem. A, 117, 2138 (2013)

    The photoionization of Cr at excited states is investigated using a velocity-map photoelectron imaging technique. Benzene chromium carbonyl or bis(6- benzene) chromium was used as a precursor for the generation of excited Cr atoms. The a5S2 x53 and a5D3 y52 transitions are then employed for the preparation of resonant intermediate states in a two-color two-photon ionization process, in which an electronic configurational change from 3d4(5D)4s4p(1P°) to 3d44s(6DJ+) occurs. The photo- electron kinetic energy distribution is found to be very sensitive to the ionization energy and the total angular momentum quantum number of the chromium ion (J+). Anisotropy parameters associated with departing electrons also show significant variation depending on the energy and total angular momentum quantum number, suggesting that direct and/or indirect ionization should be quantum-mechanically mixed, manifesting the complicated nature of angular momentum couplings in the ionization continuum.



   Jun-Ho Yoon, Jeong Sik Lim, Kyung Chul Woo, Myung Soo Kim, and Sang Kyu Kim


"Chemical Substitution Effect on Energetic and Structural Differences between
Ground and First Electronically Excited States of Thiophenoxyl Radicals

Bull. Korean Chem. Soc., 34, 415 (2013)

    Effect of chemical substitution at the para-position of the thiophenoxyl radical has been theoretically investigated in terms of energetics, structures, charge densities and orbital shapes for the ground and first electronically excited states. It is found that the adiabatic energy gap increases when CH3 or F is substituted at the para-position. This change is attributed to the stabilization of the ground state of thiophenoxyl radical through the electron-donating effect of F or CH3 group as the charge or spin of the singly-occupied molecular orbital is delocalized over the entire molecule especially in the ground state whereas in the excited state it is rather localized on sulfur and little affected by chemical substitutions. Quantitative comparison of predictions based on four different quantum-mechanical calculation methods is presented.




   Doo-Sik Ahn, Jeongmook Lee, Young Choon Park, Yoon Sup Lee, and Sang Kyu Kim


"Nuclear motion Captured by the slow electron velocity imaging  technique
in the tunnelling predissociation of the S1 methylamines

J. Chem. Phys., 136, 024306 (2012)

    Predissociation dynamics of methylamines (CH3NH2 and CH3ND2) on the first electronically excitedstates are studied using the slow-electron velocity imaging method to unravel the multi-dimensional nature of the N–H(D) chemical bond dissociation reaction which occurs via tunnelling. The nearly free internal rotation around the C–N bond axis is found to be strongly coupled to the reaction pathway, revealing nuclear motions actively involved in the tunnelling process on the S1 potential energy surfaces. The vibrational state-resolved energy and angular distributions of photoelectron, ejected from the ionization mediated by the metastable intermediate S1 state provide a unique way for mapping the predissociative potential energy surfaces.



  Songhee Han, Hyun Sik Yoo, Doo-Sik Ahn, Young S. Choi, and Sang Kyu Kim


"Vacuum ultraviolet mass-analyzed threshold ionization spectroscopy of
methylcyclohexane in the supersonic jet"

Chem. Phys. Lett., 518, 38 (2011)

    Vacuum ultraviolet (VUV) mass-analyzed threshold ionization (MATI) spectrum of supersonically cooled methylcyclohexane has been obtained to give the precise adiabatic ionization energy of 9.6958 ± 0.0025 eV for the chair equatorial conformer. Vibrationally resolved MATI spectrum has been analyzed with the aid of density functional theory and Franck–Condon calculations. The MATI spectrum reflects the structural change upon ionization and its origin is discussed by inspecting the shapes of the valence orbitals involved in the ionization process. The spectroscopic implication of the structural interconversion above the certain energy level is discussed with theoretical calculations of molecular structures and energetics.



   Kuk Ki Kim, Daehyun Kim, Sang Kyu Kim, Seung Min Park, Jae Kyu Song


"Formation of ZnO nanoparticles by laser ablation in neat water"

Chem. Phys. Lett., 511, 116-120 (2011)

    Zinc oxide (ZnO) nanoparticles were prepared in neat deionized water by laser ablation with various ablation times (10 – 40 min), fluences (50 – 130 mJ/pulse), and wavelengths (1064, 532, and 355 nm). The size and shape of the nanoparticles were affected only slightly by the ablation time and fluence at a wavelength of 1064 nm, which was explained by a dynamic formation mechanism with surface charge effects. The nanoparticles formed by ablation at 355 nm had a distinctive wire-shape with a small diameter, which was attributed to a continuous fragmentation and formation mechanism.




   SongHee Han, Hyun Sik You, Sang Kyu Kim


"Comformer-specific Ionization Spectroscopy of Bromocyclohexane:
Equatorial versus Axial conformers"

J. Phys. Chem. A, 2010, 114, 10005-10010

    Ionization of equatorial and axial conformational isomers of the chair-bromocyclohexane is investigated with use of the vacuum ultraviolet mass-analyzed threshold ionization (MATI) spectroscopic technique. Two distinct ionization energies of 9.8308 ± 0.0025 and 9.8409 ± 0.0025 eV are determined for equatorial or axial conformers, respectively. From the conformer-selective vibrational analysis, it is found that the equatorial conformer undergoes a drastic structural change upon ionization especially along the C-Br distortion mode, whereas the axial conformer shows the modest change along the ring-puckering mode with ionization, corresponding to the reaction coordinate for the conformational interconversion. Density functional theory (DFT) calculations with and without considering the spin-orbit coupling provide the appropriate mode assignments for the vibrational bands active in the ionization spectra. Natural bond orbital (NBO) analysis is carried out to give insights into the contribution of the anomeric effect to the structure-energy relationship in each conformational isomer.



  Ki Young Yeon, Dahyi Jeong, Sang Kyu Kim


"Intrinsic lifetimes of the Soret bands of the free base tetraphenylporphine (H2TPP) and
Cu(II)TPP in the condensed phase"

Chem. Commun., 46, 5572-5574 (2010)

    Soret band lifetimes of the free-base tetraphenylporphine (H2TPP) and Cu(II) tetraphenylporphine (CuIITPP) at 408 nm have been directly measured with femtosecond (fs) resolution using the fluorescence-upconversion technique for the first time, giving = 68 ± 15 and 63 ± 15 fs, respectively, in benzene solvent.




  Songhee Han, N. Jiten Singh, Tae Yeon Kang, Kyo-Won Choi, Sunyoung Choi,
 Sun Jong Baek, Kwang S. Kim, Sang Kyu Kim


"Aromatic - interaction mediated by a metal atom: structure and ionization of the
6-benzene)chromium benzene cluster"

Phys. Chem. Chem. Phys., 12, 7648-7653 (2010)


    Aromatic – interaction in the presence of a metal atom has been investigated experimentally and theoretically with the model system of bis(6-benzene)chromium–benzene cluster (Cr(Bz)2–Bz) in which a free solvating benzene is non-covalently attached to the benzene moiety of Cr(Bz)2. One-photon mass-analyzed threshold ionization (MATI) spectroscopy and first principles calculations are employed to identify the structure of Cr(Bz)2–Bz which adopts the parallel-displaced configuration. The decrease in ionization potential for Cr(Bz)2–Bz compared with Cr(Bz)2, resulting from the increase of the cation– stabilization energy upon ionization, is consistent with the parallel-displaced structure of the cluster. Theoretical calculations give the detailed cluster structures with associated energetics, thus revealing the nature of ––metal or ––cation interactions at the molecular level.



  Jeong Sik Lim, Sang Kyu Kim


"Experimental probing of conical intersection dynamics in the photodissociation of thioanisole"

Nature Chemistry, 2, 627-632 (2010)

    Direct experimental probing of conical intersections is rare but here, in studies of the photodissociation of thioanisole, a striking dependence of the non-adiabatic transition probability on photoexcitation energy has been observed, revealing the nuclear configuration of the conical intersection and its dynamic role in such transitions.



  Doo-Sik Ahn, So-Yeon Kim, Goo-Il Lim, Sungyul Lee, Young S. Choi, Sang Kyu Kim


"Mode-Dependent Fano Resonances Observed in the Predissociation of Diazirine in the S1 State"

Angew. Chem. Int. Ed., 49, 7, 1244-1247 (2010) (selected as a VIP)

    Lights, spectrometer, action: Crucial information about the detailed shape of the potential-energy surface in the vicinity of the transition state is obtained from the Fano resonances in the photodissociation cross-section of diazirine in the S1 state. The excitation along the asymmetric C-N stretching mode accelerates the ring-opening reaction, suggesting that two C-N bonds of the excited diazirine break in a stepwise manner (see scheme).



  Songhee Han, Tae Yeon Kang, Sang Kyu Kim


"Rotationally resolved spectroscopy of the 2A1 math 2B1 transition of H2S+ above the barrier to linearity
using the mass-analyzed threshold ionization photofragment excitation technique"

J. Chem. Phys., 132, 124304 (2010)


    The 2A1 math2B1 transitions of H2S+ above the barrier to linearity have been investigated with the energy resolution high enough to identify individual rotational transition lines for the first time. The rotational cooling of the cation is achieved either by the direct ionization or mass-analyzed threshold ionization (MATI) technique employed in the vacuum-ultraviolet laser excitation of the jet-cooled H2S. Subsequent photoexcitation leads to the H2S+ H2 + S+ dissociation and the S+ product yield taken as a function of the excitation energy gives the photofragment excitation (PHOFEX) spectra. The combined use of MATI and PHOFEX techniques greatly simplifies the spectrum allowing the accurate identification of the rotationally resolved bands which is otherwise a formidable task due to the intrinsic complexity of the 2A1 math 2B1 transition. Highly excited states of (0,7,0), (0,8,0), and (0,9,0) vibronic levels with different K quantum numbers which are located above the barrier to linearity are thoroughly investigated. The bent-to-quasilinear transition of H2S+ above the barrier to linearity shows the characteristics of the Renner–Teller effect, showing the large A rotational constant and strong intensity borrowing of the highly vibrationally excited ground levels such as math(0,23,0) or math(0,24,0) in the dipole-allowed excitation. Spectroscopic parameters of term values, rotational, and spin-orbit coupling constants are precisely determined in this work, providing the most quantitative spectroscopic structure of the H2S+ to date. Quantum-state dependent photodissociation dynamics are also discussed from spectral features of PHOFEX.




Oleg Kostko, Sang Kyu Kim, Stephen R. Leone, Musahid Ahmed, "Mass-Analyzed Threshold Ionization (MATI) Spectroscopy of Atoms and Molecules Using VUV Synchrotron Radiation", J. Phys. Chem. A, 113, 14206-14211 (2009).[PDF]

Jeong Sik Lim, Heechol Choi, Ivan S. Lim, Seong Byung Park, Yoon Sup Lee, Sang Kyu Kim, "Photodissociation Dynamics of Thiophenol-d1: The Nature of Excited Electronic States along the S-D Bond Dissociation Corrdinate", J. Phys. Chem. A, 113, 10410-10416 (2009).[PDF]




Kyoung-Seok Lee, Ki Young Yeon, Kyung-Hoon Jung, Sang Kyu Kim, "Direct observation of the primary and secondary C-Br bond cleavages from the 1,2-dibromopropane photodissociation at 234 and 265 nm using the velocity map ion imaging technique", J. Phys. Chem. A, vol.112, 9312-9317 (2008).[PDF]

Kyo-Won Choi, Sunyoung Choi, Doo-Sik Ahn, Songhee Han, Tae Yeon Kang, Sun Jong Baek, Sang Kyu Kim, "Clustering dynamics of the metal-benzene sandwich complex: the role of microscopic structure of the solute in the bis(6-benzene)chromium·Arn clusters (n= 1-15)", J. Phys. Chem. A, 122, 7125-7127 (2008).[PDF]

Doo-Sik Ahn, Kyo-Won Choi, Sun Jong Baek, Young S. Choi, Sungyul Lee, Heechol Choi, Kyoung Koo Baeck, Sang Kyu Kim, "Structure of Pyridazine in the S1 state: Experiment and Theory", ChemPhysChem, 9, 1610-1616 (2008)[PDF]

Sunyoung Choi, Kyo-Won Choi, Songhee Han, Doo-Sik Ahn, Tae Yeon Kang, Sun Jong Baek, Sang Kyu Kim, "Conformationally specific vacuum-ultraviolet mass-analyzed threshold ionization spectroscopy of alkanethiols: structure and ionization of conformational isomers of ethanethiol, isopropanethiol, 1-propanethiol, tert-butanethiol, and 1-butanethiol", J. Phys. Chem. A, 122, 7191-7199 (2008).[PDF]

Doo-Sik Ahn, Jeongmook Lee, Jeong-Mo Choi, Kyoung-Seok Lee, Sun Jong Baek, Kunhye Lee, Kyoung-Koo Baeck, Sang Kyu Kim, "State-selective predissociation dynamics of methylamines: the vibronic and H/D effects on the conical intersection dynamics", J. Chem. Phys., 128, 224305 (2008).[PDF]

Sunyoung Choi, Tae Yeon Kang, Kyo-Won Choi, Songhee Han, Doo-Sik Ahn, Sun Jong Baek, and Sang Kyu Kim, "Ionization spectroscopy of conformational isomers of propanal: the origin of the conformational preference", J. Phys. Chem. A., 112, 5060–5063 (2008).[PDF]

Songhee Han, Tae Yeon Kang,  Sunyoung Choi, Kyo-Won Choi, Sun Jong Baek, Sungyul Lee  and Sang Kyu Kim, One-photon ionization spectroscopy of jet-cooled oxazole and thiazole: the role of oxygen and sulfur in the -conjugation of heterocyclic compounds Phys. Chem. Chem. Phys., 10, 3883 – 3887 (2008).[PDF]

Hoon Han, Seong Byeong Park, Sang Kyu Kim, and Sukbok Chang, Copper-Nitrenoid Formation and Transfer in Catalytic Olefin Aziridination Utilizing Chelating 2-Pyridylsulfonyl Moieties, J. Org. Chem., 73, 2862 – 2870 (2008).[PDF]

Jeong Sik Lim, Yoon Sup Lee, and Sang Kyu Kim, "Control of the Intramolecular orbital alignment observed in the photodissociation of thiophenol: the conformational manipulation via the chemical substitution", Angew. Chem. int. ed., 47, 10, 1853-1856 (2008) (selected as a VIP). [PDF]



Ho-Sung Kim, Doo-Sik Ahn, Sang-Yoon Chung, Sang Kyu Kim, SungyulLee, Tautomerization of adenine facilitated by water: Computational study of microsolvation, J. Phys. Chem. A, 111 (32), 8007, (2007). [PDF]

Kyo-Won Choi, Doo-Sik Ahn, Joo-Hee Lee, and Sang Kyu Kim, A conformationally specific alpha- and beta-alanine decarboxylation pathway, Chem. Commun. (9) 1041, (2007). [PDF]

Ivan S. Lim, Jung Sik Lim, Yoon Sup Lee, and Sang Kyu Kim, Experimental and theoretical study of photodissociation reaction of thiophenol at 243 nm: observation of the intramolecular orbital alignment, J. Chem. Phys., 126, 034306, (2007). [PDF]

Kyo-Won Choi, Sunyoung Choi, Sun Jong Baek and Sang Kyu Kim, Pulsed-field ionization spectroscopy of high Rydberg states (n = 50-200) of Bis(6-benzene)chromium, J. Chem. Phys., 126, 034308, (2007). [PDF]




Sunyoung Choi, Kyo-Won Choi, Sang Kyu Kim, Sangyoon Chung, and Sungyul Lee, Vibrational Structures of Dimethyl sulfide and Ethylene sulfide cations studied by Vacuum-UV mass-analyzed threshold ionization (MATI) spectroscopy J. Phys. Chem. A, 110, 13183, (2006). [PDF]

Ji Min Lee, Doo-Sik Ahn, Doo Young Jung, Junseung Lee, Youngkyu Do, Sang Kyu Kim, and Sukbok Chang, "Hydrogen-Bond-Directed Highly Stereoselective Synthesis of Z-Enamides via Pd-Catalyzed Oxidative Amidation of Conjugated Olefins", J. Am. Chem. Soc., 128, 12954, (2006). [PDF]

 Jeong Sik Lim, Ivan S. Lim, Kyoung-Seok Lee, Doo-Sik Ahn, Yoon Sup Lee, and Sang Kyu Kim, "Intramolecular orbital alignment observed in the photodissociation of thiophenol-d1", Angew. Chem. int. ed., 45, 6290, (2006) [PDF]

 Min Hee Park, Kyo-Won Choi, Sunyoung Choi, and Sang Kyu Kim, "Vibrational structures of methylamine isotopomers in the predissociative à states: CH3NHD, CD3NH2, CD3NHD, and CD3ND2", J. Chem. Phys., 125, 084311, (2006) [PDF]

 Kyo-Won Choi, Doo-Sik Ahn, Joo-Hee Lee, Sang Kyu Kim, Vibrational Spectroscopy of the Pyridazine Cation in the Ground State, J. Phys. Chem. A., 110 (8), 2634, (2006). [PDF]

 Kyoung-Seok Lee, Jung-Sik Lim, Doo Sik Ahn, Kyo-Won Choi, Sang Kyu Kim, Young S. Choi, Nonadiabatic Dynamics in the Photodissociation of ICH2CN at 266 and 304 nm Using a Velocity Map Ion Imaging Technique, J. Chem. Phys., 124, 124307, (2006). [PDF]

 Kyo-Won Choi, Joo-Hee Lee, Sang Kyu Kim, Vacuum-Ultraviolet Ionization Spectroscopy of the Jet-Cooled RNA-Base Uracil, Chem. Commun., 1, 78, (2006). [PDF]




 Kyo-Won Choi, Joo-Hee Lee, Sang Kyu Kim, "Ionization Spectroscopy of a DNA Base: Vacuum-Ultraviolet Mass-Analyzed Threshold Ionization Spectroscopy of Jet-Cooled Thymine", J. Am. Chem. Soc.(Communication), 127, 15674, (2005).  [PDF]

 In-Sun Jeon, Doo-Sik Ahn, Sung-Woo Park, Sungyul Lee, and S. K. Kim, "Structures and isomerization of serine in aqueous solution: Computational study", Chem. Phys. Lett., 403, 72-76 (2005). [PDF]

 Doo-Sik Ahn, Ae-Ri Kang, Sungyul Lee, Bongsoo Kim, Daniel Neuhauser, and S. K. Kim, "On the stability of glycine-water clusters with excess electron: Implications for photoelectron spectroscopy", J. Chem. Phys., 122, 84310 (2005). [PDF]  

 Kyo-Won Choi, Doo-Sik Ahn, Sungyul Lee, and S. K. Kim, "One-Photon Mass-Analyzed Threshold Ioniization Spectroscopy of Bis(6-benzene)chromium and Its benzene and Ar Clusters", J. Phys. Chem. A, 108, 11292-11295 (2004). [PDF]  

 K.-W. Choi, D.-S. Ahn, S. Lee, H. Choi, K.-K. Baeck, S.-U. Heo, S. J. Baek, Y. S. Choi, and S. K. Kim, Structural Distortion of Pyridazine in the 1(n,*) Excited State: Evidence for Local Excitation, Chem. Phys. Chem., 5, 737-739 (2004). [PDF] 

 S. Y. Chae, M. K. Park, S. K. Lee, T. Y. Kim, S. K. Kim, and W. I. Lee, Preparation of size-controlled TiO2 nanoparticles and derivation of optically transparent photocatalytic films, Chem. Mater., 15, 3326-3331 (2003). [PDF]  

 Y. Masumoto, S. K. Kim, T. Suzuki, Femtosecond photoelectron imaging study of pyridazine: S1 lifetime and (3s,3p) Rydberg state energetics, J. Chem. Phys., 119 (1), 300-303 (2003). [PDF]  

 S. J. Baek, K.-W. Choi, Y. S. Choi, and S. K. Kim, Spectroscopy and dynamics of methylamine II: rotational and vibrational structures of CH3NH2 and CH3ND2 in cationic D0 states J. Chem. Phys., 118 (24), 11040-11047 (2003). [PDF]  

 S. J. Baek, K.-W. Choi, Y. S. Choi, and S. K. Kim, Spectroscopy and dynamics of methylamine I: rotational and vibrational structures of CH3NH2 and CH3ND2 in à states J. Chem. Phys., 118 (24), 11026-11039 (2003). [PDF]  

 S. J. Baek, K.-W. Choi, Y. S. Choi, and S. K. Kim, First excited and cationic ground states of jet-cooled 2-aminopyridines · Arn (n=1,2) clusters: energetics and structures, J. Phys. Chem. A, 107 (24), 4826-4828 (2003). [PDF]  

 S. J. Baek, K.-W. Choi, Y. S. Choi, and S. K. Kim, Vibrational structures of predissociating methylamines (CH3NH2 and CH3ND2) in àstates: Free internal rotation of CH3 with respect to NH2, J. Chem. Phys., 117 (22), 10057 (2002).  [PDF]

 S. J. Baek, K.-W. Choi, Y. S. Choi, and S. K. Kim, Resonant-enhanced two-photon ionization and mass-analyzed threshold ionization spectroscopy of jet-cooled 2-aminopyridines (2AP-NH2, -ND2, -NHD, and -NDH), J. Chem. Phys., 117(5), 2131-2140 (2002).  [PDF]

 S. J. Baek, D. Lee, K.-W. Choi, Y. S. Choi, and S. K. Kim, Torsional vibrational levels combined with higher frequency modes of the jet-cooled p-methoxybenzyl alcohol in the S1 excited state, J. Mol. Structure, 611(1-3), 203-211 (2002).  [PDF]

 T. S. Kim, K.-W. Choi, S. K. Kim, Y. S. Choi, S. W. Park, D. S. Ahn, S. Lee, and K. Yoshihara, Fluorescence excitation spectroscopy of octatetraene-Xe van der Waals clusters, Bull. Korean Chem. Soc., 23(2), 195-200 (2002). [PDF]

 D. Lee, S. J. Baek, K.-W. Choi, Y. S. Choi, and S. K. Kim, Resonantly-enhanced two-photon ionization and mass-analyzed threshold ionization (MATI) spectroscopy of 2-hydroxypyridine, Bull. Korean Chem. Soc., 23(2), 277-280 (2002). [PDF]

 S. T. Park, S. K. Kim, M. S. Kim, Observation of conformation-specific pathways in the photodissociation of 1-iodopropane ions, Nature, 415, 306-308 (2002).  [PDF]

 W.-H. Park, S. H. Cho, H. Cho, S. K. Kim, and Y. S. Choi, Ultraviolet Photolysis of 1,6-Methano[10]annulene Generates the Singlet Methylene, Bull. Korean Chem. Soc. 22(9), 1030-1032 (2001). [PDF]

 S. K. Shin, S. K. Kim, H. L. Kim, and C. R. Park, Two photon dissociation of acetone, acetaldehyde, and acetic acid at 243 nm: translational energy release in the H atom channel, J. Photochemistry and Photobiology A: Chemistry 143, 11-16 (2001). [PDF]

 H. T. Kwon, S. K. Shin, S. K. Kim, H. L. Kim, and C. R. Park, Photodissociation dynamics of acetic acid and trifluoroacetic acid at 193 nm, J. Phys. Chem. A 105 (28), 6775-6779 (2001).[PDF]

 S. T. Park, S. K. Kim, and M. S. Kim, Vacuum-ultraviolet mass-analysed threshold ionization spectra of iodobutane isomers: conformer-specific ionization and ion-core dissociation followed by ionization, J. Chem. Phys. 115 (6), 2492-2498 (2001). [PDF]

 S. T. Park, S. K. Kim, and M. S. Kim, One-photon mass-analysed threshold ionization spectroscopy of 1- and 2-iodopropanes in vacuum ultraviolet, J. Chem. Phys. 114 (13), 5568-5576 (2001). [PDF]





S. H. Cho, W.-H. Park, S. K. Kim, and Y. S. Choi, "Unimolecular dissociation dynamics of vinyl chloride on the ground      potential energy surface: the method of excitation and product state distributions of HCl and Cl fragments, J. Phys.      Chem. A. 104(45), 10482-10488 (2000). [PDF]


M.-C. Yoon, S. J. Baek, H. Cho, Y. S. Choi, S. K. Kim, "Supersonic jet spectroscopic study of p-methoxybenzyl

     alcohol", J. Phys. Chem. A. 104(45), 10173-10178 (2000). [PDF]


M.-C. Yoon, Y. S. Choi, S. K. Kim, "The OH product state distribution from the photodissociation of      hexafloroacetylacetone", J. Phys. Chem. A, 104(19), 4352-4355 (2000).   Chem. Phys. (Commu), 111, 456-459 (1999).



G.-I. Lim, S.-M. Lim, S. K. Kim, and Young S. Choi, "Unexpectedly large O37ClO/O35ClO intensity ratios of the      fluorescence from the low-energy vibrational levels of OClO (A2A2)", J. Chem. Phys. (Commu), 111, 456-459 (1999).      [PDF]


M.-C. Yoon, Y. S. Choi, S. K. Kim, "Photodissociation Dynamics of acetylacetone: the OH product state distribution", J.      Chem. Phys. 110, 11850-11855 (1999). [PDF]


S.-M. Lim, G.-I. Lim, T.-S. Kim, S. K. Kim, Y. S. Choi, "Fluorescence excitation spectrum of OClO (A2A2)", J. Phys.      Chem. A, 103 (13), 2097-2099 (1999). [PDF]


M.-C. Yoon, Y. S. Choi, S. K. Kim, "Fluorescence excitation spectroscopic study of the jet-cooled acetyl cyanide", J.      Chem. Phys., 110, 7185-7191 (1999). [PDF]


G.-I. Lim, M.-C. Yoon, S.-M. Lim, T.-S. Kim, S. K. Kim, Y. S. Choi, I. Kwak, "Fluorescence excitation spectroscopy of the jet-cooled dimethyldiazirine: the CH3 torsional mode assignment", Bull. Korean Chem. Soc., 20(3), 365-366 (1999).

M.-C. Yoon, Y. S. Choi, S. K. Kim, "The OH production from the -* transition of acetylacetone", Chem. Phys. Letters, 300, 207 (1999). [PDF]

T.-S. Kim, S. K. Kim, Y. S. Choi, I. Kwak, "Laser-Induced Fluorescence Spectroscopy of the S1-S0 (1B2-1A1) Transition of Dimethyldiazirine", Bull. Korean Chem. Soc. 19, 1042 (1998).

S.-M. Lim, T.-S. Kim, G.-I. Lim, S. K. Kim, Y. S. Choi, "Direct formation of CH2(b1B1) in the near-UV photodissociation of diazirine", Chem. Phys. Letters 288, 828 (1998).[PDF]


T.-S. Kim, S. K. Kim, Y. S. Choi, I. Kwak, "On the second electronic state near the S1 state in dimethyldiazirine",J.      Chem. Phys. 107, 8719 (1997). [PDF]


E. A. Wade, H. Clauberg, S. K. Kim, A. Mellinger, C. B. Moore, "Dynamics of Rotational Energy Release for Dissociation of Singlet Ketene and the Singlet/Triplet Branching Ratio", J. Phys. Chem. A 101, 732 (1997). [PDF]


S. K. Kim, E. R. Lovejoy, C. B. Moore, "Dynamics at Unimolecular Transition States", in Gas-Phase Chemical

  Reaction  Systems: Experiments and Models 100 Years after Max Bodenstein, ed. by J. Wolfrum, H.-R. Volpp, R. Rannacher, J. Warnatz, Springer Series in Chemical Physics No.61 (Springer Berlin, Heidelberg, 1996) p.67.


S. K. Kim, J. Guo, J. S. Baskin, A. H. Zewail, "Femtosecond Chemically Activated Reactions: Concept of Nonstatistical      Activation at High Thermal Energies", J. Phys. Chem. 100, 9202 (1996). [PDF]


S. K. Kim, A. H. Zewail, "Femtosecond elementary dynamics of transition states and asymmetric -cleavage in Norrish      reaction", Chem. Phys. Letters 250, 279 (1996). [PDF]





A. Douhal, S. K. Kim, A. H. Zewail, "Femtosecond molecular dynamics of tautomerization in model base pairs", Nature 378, 260 (1995). [PDF]


S. K. Kim, S. Pedersen, A. H. Zewail, "Direct Femtosecond Observation of the Transient Intermediate in the -Cleavage      Reaction of (CH3)2CO to 2CH3 + CO: Resolving the Issue of Concertedness", J. Chem. Phys. 103, 477 (1995). [PDF]


S. K. Kim, J. J. Breen, D. W. Willberg, L. W. Peng, A. Heikal, J. A. Syage, A. H. Zewail, "Solvation Ultrafast Dynamics of      Reactions 8: Acid-Base Reactions in Finite-Sized Clusters of Naphthol in Ammonia, Water, and Piperidine", J. Phys.      Chem. 99, 7421 (1995). [PDF]


S. K. Kim, S. Pedersen, A. H. Zewail, "Femtochemistry of Organometallics: Dynamics of Metal-Metal and Metal-Ligand      Bond Cleavage in M2(CO)10", Chem. Phys. Letters 233, 500 (1995). [PDF]


S. K. Kim, E. R. Lovejoy, C. B. Moore, "Transition-State Vibrational Level Thresholds for the Dissociation of Triplet      Ketene", J. Chem. Phys. 102, 3202 (1995). [PDF]


S. K. Kim, J.-K. Wang, A. H. Zewail, "Femtosecond pH jump: Dynamics of Acid-Base Reactions in Solvent Cages",

     Chem. Phys. Letters 228, 369 (1994). [PDF]


E. R. Lovejoy, S. K. Kim, C. B. Moore, "Observation of Transition-State Vibrational Thresholds in the Rate of Dissociation of Ketene", Science 256, 1541 (1992). [PDF]


E. R. Lovejoy, S. K. Kim, R. A. Alvarez, C. B. Moore, "Kinetics of Intramolecular Carbon Atom Exchange in Ketene", J.      Chem. Phys. 95, 4081 (1991). [PDF]


S. K. Kim, Y. S. Choi, C. D. Pibel, Q.-K. Zheng, C. B. Moore, "Determination of the Singlet/Triplet Branching Ratio in the      Photodissociation of Ketene", J. Chem. Phys. 94, 1954 (1991). [PDF]


C. B. Moore, Q.-K. Zheng, Y. S. Choi, W. H. Green, S. K. Kim, A. J. Mahoney, W. H. Miller, C. D. Pibel, W. F. Polik, P.      Teal, "The High-Resolution Spectroscopy of Dissociating Molecules", Phil. Trans. R. Soc. Lond. A 332, 297 (1990).


S. K. Kim, M. S. Kim, S. W. Suh, "Surface-Enhanced Raman Scattering (SERS) of Aromatic Amino Acids and their Glycyl      Peptides", Journal of Raman Spectroscopy 18, 171 (1987).


S. K. Kim, T. H. Joo, S. W. Suh, M. S. Kim, "Surface-Enhanced Raman Scattering (SERS) of Nucleic Acids: Adenine      Series", Journal of Raman Spectroscopy 17, 381 (1986).


K. W. Kim, S. K. Kim, M. S. Kim, S. W. Suh, "Raman Spectroscopic study of 5'-rGMP sol", Biopolymers 25, 753 (1986).


S. B. Hong, S. K. Kim, M. S. Kim, S. W. Suh, "The Preliminary X-ray and Raman Study of GramicidinS:HCl", Archives of      Biochemisty and Biophysics 243, 563 (1985).


S. K. Kim, M. S. Kim, S. W. Suh, "Kinetics of Hydrogen/Deuterium Exchange in 8-CH of 5-rAMP", Bulletin of Korean      Chemical Society 6, 270 (1985).