Koichi Ohno

National Institute of Informatics, Edo, Tōkyō, Japan

Are you Koichi Ohno?

Claim your profile

Publications (235)642.41 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Quantum chemical calculations have predicted the existence of a new carbon family with double-layered structures formed by arranging prism-C2n (n = 6, 8, and 12) units. Theoretical explorations of potential energy surfaces suggest the lowest barriers of the reaction channels to be ca. 30 kJ mol−1 for a D2h prism-C16 dimer and a D3h prism-C24 trimer. Geometry optimizations under periodic boundary conditions yield some prism-C2n sheets composed of CC single bonds of ca. 0.15–0.16 nm. The relative energies per one atom with respect to graphene are 90–160 kJ mol−1. Van der Waals thickness is estimated to be ca. 0.5 nm.
    Chemical Physics Letters 07/2015; 633. DOI:10.1016/j.cplett.2015.05.024 · 1.99 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The thermodynamics and dynamics of a carbonaceous molecular bearing comprising a belt-persistent tubular molecule and a fullerene molecule have been investigated using density functional theory (DFT). Among ten representative methods, two DFT methods afforded an association energy that reasonably reproduced the experimental enthalpy of −12.5 kcal mol−1 at the unique curved π-interface. The dynamics of the molecular bearing, which was assembled solely with van der Waals interactions, exhibited small energy barriers with maximum values of 2–3 kcal mol−1 for the rolling motions. The dynamic motions responded sensitively to the steric environment and resulted in two distinct motions, precession and spin, which explained the unique NMR observations that were not clarified in previous experimental studies.
    Chemical Science 02/2015; 6(5). DOI:10.1039/C5SC00335K · 8.60 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: The photodissociation of small molecules occurs upon irradiation by ultraviolet or visible light and it is a very important chemical process in Earth's atmosphere, the atmospheres of other planets, and in interstellar media. Photodissociation is an important method used to thoroughly investigate the fundamental issues of chemical reactivity. Photodissociation involves molecules and reaction fragments moving over ground and exited state potential surfaces (PESs). Molecules can move on a single PES (adiabatic pathway) and they can also cross over from one PES to another in nonadiabatic pathways. For a full theoretical understanding of a photodissociation mechanism, all the important nonadiabatic and adiabatic pathways must be determined. This is not an easy task. We have developed an efficient computational method referred to as the global reaction route mapping (GRRM) strategy that allows for a theoretical exploration of ground and excited state PESs and their crossing seams in an automatic manner. In this article, we summarize our approaches and present examples of the application together with newly determined chemical insights. These include the complex photodissociation mechanism of the formaldehyde H2CO molecule, the exclusive excited state roaming dynamics of the nitrate NO3 radical, and all product channels and conformational memory in the photodissociation of the formic acid HCOOH molecule. Finally, perspectives for the theoretical design of photofunctional molecules are discussed.
    Journal of the American Chemical Society 02/2015; 137(10). DOI:10.1021/ja512394y · 11.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Isomers of benzene (C6H6) have been searched by quantum chemical calculations using the GRRM/SCC-DFTB program. Further optimization at the level of B3LYP/6-311G(d, p) gave 2004 equilibrium structures (EQ). Obtained EQs were assigned as 212 valence isomers, 928 non-valence isomers, 798 two-component clusters, and 66 three-component clusters. Energies of EQs range from the most stable isomer of benzene to the highest EQ at 1237 kJ/mol. The low energy region below 380 kJ/mol only includes valence isomers. Valence isomers are distributed between 0 and 807 kJ/mol, while non-valence isomers are located in the range of 380 - 1180 kJ/mol. All of the experimentally known 30 isomers of benzene were searched as valence isomers by the ADDF/SCC-DFTB method. Formally hypervalent molecules including pentacoordinated carbon atoms were discovered among non-valence isomers.
    Bulletin of the Chemical Society of Japan 01/2015; DOI:10.1246/bcsj.20150088 · 2.22 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Methyltrioxorhenium (MTO)-catalyzed transfer of a methylene group to styrene has been computationally found to preferably follow a stepwise mechanism to give phenylcyclopropane via formation of a pseudo-metallacyclic intermediate and subsequent alkylative cyclization. The present result serves as the first theoretical evidence for d0 transition metal mediated transfer of methylene as a terminal form rather than a metal carbene or carbenoid fashion, accompanied by the cleavage of a H2C═O double bond. The mechanism presented here is in contrast to the carbenoid or metal carbene promoted methylene transfer and to the MTO-catalyzed isoelectronic atom (group) transfer in MeRe(O)2(η2-O–NH) or MeRe(O)2(η2-O–O). This study not only enriches the chemistry of olefin cyclopropanation and the MTO-catalyzed group (atom) transfer event but also sheds new light on the reaction chemistry of formaldehyde.
    Organometallics 07/2014; 33(14):3840-3846. DOI:10.1021/om500560f · 4.25 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A new 2,3‐disila‐1,3‐butadiene (3) was synthesized as pale yellow crystals by a double sila‐Peterson reaction of 1,1,2,2‐tetrasilyl‐1,2‐dilithiodisilane with two equivalents of 2‐adamantanone at 0 °C. In the solid state, the two SiC bonds adopt a synclinal conformation with a dihedral angle of 76.8(1)°. UV/Vis spectra show two distinct absorption bands, assignable to the π(SiC)→π*(SiC) transition, at 371 and 322 nm and the former is considerably redshifted compared with that of structurally similar silenes. The 2,3‐disilabutadiene isomerizes to the corresponding 1,3‐disilabicyclo[1.1.0]butane with the activation parameters of ΔH ≠=74.5±5.4 kJ mol−1 and ΔS ≠=−71.1±17.1 J mol−1 K−1. DFT studies suggest that the isomerization proceeds through a conrotatory route rather than a disrotatory route. H2O and 9,10‐phenanthrenequinone added across each SiC bond in the 2,3‐disila‐1,3‐butadiene. The UV/Vis spectrum and reactivity of 3 suggest that the interaction between the two SiC bonds in 3 would be significant but rather small compared with that between SiSi bonds in a synclinal tetrasilabutadiene. A new 2,3‐disila‐1,3‐butadiene was synthesized as pale yellow crystals by a double sila‐Peterson reaction. Although the two SiC bonds adopt a synclinal conformation with a dihedral angle of 76.8(1)°, the redshifted longest absorption band maxima assignable to the π(SiC)→π*(SiC) transition at 371 nm suggests considerable interaction between two SiC bonds. The 2,3‐disila‐1,3‐butadiene is thermally unstable and isomerizes to 1,3‐disilabicyclo[1.1.0]butane (see scheme).
    Chemistry 07/2014; 20(30). DOI:10.1002/chem.201402868 · 5.70 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Huge numbers of structures, 7000 isomers and 26229 transition structures, have been searched for C6H6 in quantum chemical calculations by using a GRRM/SCC-DFTB program. The stability of benzene is outstanding. At B3LYP/6-311G(d,p) level, no isomers are found in a wide energy range of 260 kJ mol−1 above the energy of benzene, except for fulvene at 148 kJ mol−1. Other isomers are distributed between 260–1250 kJ mol−1. Thirty experimentally known isomers are found in the energy range below ca. 600 kJ mol−1.
    Chemistry Letters 05/2014; 43(5):702-704. DOI:10.1246/cl.140024 · 1.30 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: A direct reaction pathway for water gas shift reaction (WGSR) in gas phase, H2O + CO -> H-2 + CO2, was discovered by using anharmonic downward distortion following method. The direct WGSR is accompanied by a roaming-like mechanism. To examine the initial conditions of the direct WGSR, we carried out ab initio molecular dynamics simulations and showed that cooperative excitations of OH-stretching vibrational modes and the orientational control of reactants are required for the direct WGSR.
    Chemistry Letters 02/2014; 43(2):193-195. DOI:10.1246/cl.130940 · 1.30 Impact Factor
  • Bulletin of the Chemical Society of Japan 01/2014; DOI:10.1246/bcsj.20140189 · 2.22 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: An anthryl-substituted exocyclic silene, 3-silylene-2-silaaziridine, was synthesized by isomerization of the corresponding disilacyclopropanimine. The UV-vis spectrum of the silene shows a distinct intramolecular charge transfer (ICT) transition from the pi orbital of the Si=C double bond to the pi* orbital of the anthryl moiety. The relatively high-lying pi(Si=C) orbital of the 3-silylene-2-silaaziridine moiety and the low-lying pi* orbital of the anthryl group would be responsible for the distinct ICT band.
    Journal of the American Chemical Society 07/2013; 135(29). DOI:10.1021/ja404045f · 11.44 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In order to investigate outer valence ionic states of open-shell metallocenes, we have applied two-dimensional collision-energy/electron-energy-resolved Penning ionization electron spectroscopy (2D-PIES) upon collision with metastable He*(2(3)S) excited atoms as well as a high level ab initio molecular orbital calculation (the partial third-order quasiparticle theory of the electron propagator (P3)) to ionization from neutral ground states of vanadocene ((4)A2g) and nickelocene ((3)A2g). Assignments of observed Penning ionization electron/He I ultraviolet photoelectron spectra were consistent with the P3 calculation results for ionization of α and β spin electrons except for electron correlation bands observed by PIES. Negative collision energy dependence of partial Penning ionization cross-sections (CEDPICS) indicate attractive interaction with He*(2(3)S) around the molecule. Results by model potential calculation utilizing Li(2(2)S) instead of He*(2(3)S) for interaction between He*(2(3)S) and open-shell metallocenes do not explain the strong negative CEDPICS of the bands observed in PIES.
    The Journal of Physical Chemistry A 03/2013; 117(14). DOI:10.1021/jp310308k · 2.78 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Global reaction route mapping (GRRM), a fully-automated search for all important reaction pathways relevant to a given purpose, on the basis of quantum chemical calculations enables systematic elucidation of complex chemical reaction mechanisms. However, GRRM had previously been limited to very simple systems. This is mainly because such calculations are highly demanding even in small systems when a brute-force sampling is considered. Hence, we have developed two independent but complementary methods: anharmonic downward distortion following (ADDF) and artificial force induced reaction (AFIR) methods. ADDF can follow reaction pathways starting from local minima on the potential energy surface (PES) toward transition structures (TSs) and dissociation channels. AFIR can find pathways starting from two or more reactants toward TSs for their associative reactions. In other words, ADDF searches for A → X type isomerization and A → X + Y type dissociation pathways, whereas AFIR finds A + B → X (+ Y) type associative pathways. Both follow special paths called the ADDF path and the AFIR path, and these tend to pass through near TSs of corresponding reaction pathways, giving approximate TSs. Such approximate TSs can easily be re-optimized to corresponding true TSs by standard geometry optimizations. On the basis of these two methods, we have proposed practical strategies of GRRM. The GRRM strategies have been applied to a variety of chemical systems ranging from thermal- and photochemical-reactions in small systems to organometallic- and enzyme-catalysis, on the basis of quantum chemical calculations. In this perspective, we present an overview of the GRRM strategies and some results of applications. Their practical usage for systematic prediction is also discussed.
    Physical Chemistry Chemical Physics 02/2013; 15(11). DOI:10.1039/c3cp44063j · 4.20 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: In theoretical studies of chemical reactions involving multiple potential energy surfaces (PESs) such as photochemical reactions, seams of intersection among the PESs often complicate the analysis. In this paper, we review our recipe for exploring multiple PESs by using an automated reaction path search method which has previously been applied to single PESs. Although any such methods for single PESs can be employed in the recipe, the global reaction route mapping (GRRM) method was employed in this study. By combining GRRM with the proposed recipe, all critical regions, that is, transition states, conical intersections, intersection seams, and local minima, associated with multiple PESs, can be explored automatically. As illustrative examples, applications to photochemistry of formaldehyde and acetone are described. In these examples as well as in recent applications to other systems, the present approach led to discovery of many unexpected nonadiabatic pathways, by which some complicated experimental data have been explained very clearly.
    Advances in Physical Chemistry 05/2012; 2012(1687-7985). DOI:10.1002/chin.201221265
  • Koichi Ohno, Satoshi Maeda
    [Show abstract] [Hide abstract]
    ABSTRACT: An efficient technique constructing anharmonic potential energy functions was applied to ab initio vibrational analysis of benzene. Anharmonic potentials including the 6-order terms, much higher than the full quartic force field, were automatically generated by a second-order algorithm using the scaled hypersphere search method, and vibrational calculations were performed at the level of VQDPT[1+2]. In comparison with previously reported anharmonic calculations, the present approach gave an excellent ab initio result for in-plane modes including the b2u so called Kekulé mode. Characteristic properties of various approaches were discussed in connection with the anharmonic effects and the strong vibronic effects.
    Chemical Physics Letters 02/2011; 503(4):322-326. DOI:10.1016/j.cplett.2011.01.021 · 1.99 Impact Factor
  • Koichi Ohno, Satoshi Maeda
    Molecular Science 01/2011; 5(1):A0042. DOI:10.3175/molsci.5.A0042
  • [Show abstract] [Hide abstract]
    ABSTRACT: ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.
    ChemInform 10/2010; 22(42). DOI:10.1002/chin.199142040
  • [Show abstract] [Hide abstract]
    ABSTRACT: The dynamics on the vacuum-ultraviolet one-photon ionization of a formamide-water cluster is investigated by a combination of theoretical reaction-path search and infrared spectroscopic methods. A keto-enol tautomerization of the formamide moiety occurs after photoionization by a catalytic action of the water molecule accompanied with its long-distance migration; the water molecule in the cluster migrates almost one turn around the formamide moiety. During the migration, the water molecule abstracts the proton of CH in the formamide moiety and carries it to the O atom side in the carbonyl group through a "catch and release"-type catalytic action.
    The Journal of Physical Chemistry A 10/2010; 114(44):11896-9. DOI:10.1021/jp107034y · 2.78 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Structural, energetic, and mechanistic features of the initial steps of the reaction of an O atom with Si(001)-(2 × 1) were modeled by the use of a Si9H12 + O system. Transition state structures (TSs) and equilibrium structures (EQs) as well as dissociation channels (DCs) were systematically searched using a global reaction route mapping (GRRM) technique on the potential energy surface (PES) based on the scaled hypersphere search (SHS) algorithm. The first six low-energy structures were consistent with known structure models for oxygen adsorption on the dimer of Si(001)-(2 × 1). Other structures with higher energies could be well interpreted as intermediates leading toward reaction paths for migration/dissociation occurring at high temperatures.
    The Journal of Physical Chemistry C 08/2010; 114(37). DOI:10.1021/jp102883c · 4.84 Impact Factor
  • [Show abstract] [Hide abstract]
    ABSTRACT: Penning ionization of iodomethane (CH3I) and diiodomethane (CH2I2) upon collision with metastable He*(23S) atoms was studied by collision-energy/electron-energy resolved two-dimensional Penning ionization electron spectroscopy (2D-PIES) over a wide range of collision energies (20 – 350 meV). Collision energy dependence of partial ionization cross sections (CEDPICS) indicates that the interaction with He*(23S) atoms around the valence molecular orbitals is attractive at low collision energies except for the only σCH molecular orbital region of iodomethane which has a repulsive character in the normal collision energy range (70 – 350 meV). Large bands at lower electron energies (3.7 – 5.5 eV) in PIES spectra were ascribed to autoionization from a transient ion-pair. The related entrance ionization channel has an attractive character. The excitation transfer, which is responsible for the I** autoionization, takes place in regions close to carbon atoms and is repulsive towards He*(23S) in the normal collision energy range. The superexcited complex of (He-CH2I2)** autoionizes via the excitation transfer occurring close to the σCI regions of the targets.
    Journal of Physics Conference Series 06/2010; 235(1):012014. DOI:10.1088/1742-6596/235/1/012014
  • S Kudo, N Kishimoto, K Ohno
    [Show abstract] [Hide abstract]
    ABSTRACT: 2,2'-bithiophene in the gas phase was studied by ultraviolet photoelectron spectroscopy (UPS) and two-dimensional Penning ionization electron spectroscopy (2D-PIES) to obtain the information of stereodynamics in Penning ionization and anisotropic interaction around the ionization region. Thiophene and the 2,2'-bithiophene layer on a Ag(110) surface were investigated by two-dimensional metastable impact electron spectroscopy (2D-MIES). From the relative intensity in the UPS and PIES spectra and the collision energy dependence of partial ionization cross sections (CEDPICS) for 2,2'-bithiophene, ionization bands were assigned to π orbitals. A comparison with the CEDPICS for a gas molecule and the molecular layer on Ag(110) revealed that the attractive interaction between He*(23S) and both thiophene and 2,2-bithiophene was weak due to the formed molecular layer.
    Journal of Physics Conference Series 06/2010; 235(1):012012. DOI:10.1088/1742-6596/235/1/012012

Publication Stats

3k Citations
642.41 Total Impact Points

Institutions

  • 2015
    • National Institute of Informatics
      Edo, Tōkyō, Japan
  • 1995–2015
    • Tohoku University
      • • Department of Chemistry
      • • Graduate School of Science
      Sendai-shi, Miyagi, Japan
  • 2009–2013
    • Toyota Physical and Chemical Institute
      Seto, Aichi, Japan
  • 1998
    • Wakayama University
      • Department of Material Science and Chemistry
      Wakayama, Wakayama, Japan
  • 1991
    • Toho University
      • Department of Biomolecular Science
      Edo, Tōkyō, Japan
  • 1980–1991
    • The University of Tokyo
      • Department of Chemistry
      Edo, Tōkyō, Japan