Koichi Ohno

Tohoku University, Miyagi, Japan

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Publications (230)630.13 Total impact

  • [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
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    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; DOI:10.1021/ja512394y · 11.44 Impact Factor
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    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
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    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
  • Bulletin of the Chemical Society of Japan 01/2014; DOI:10.1246/bcsj.20140189 · 2.22 Impact Factor
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    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
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    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
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    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
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    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. DOI:10.1002/chin.201221265
  • Koichi Ohno, Satoshi Maeda
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    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
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    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
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    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
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    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
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    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
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    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
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    ABSTRACT: Structures of transition states (TSs) and minima on seam of crossing (MSXs) for potential energy surfaces (PESs) of acetone of the S0, S1, and T1 states were explored. On the basis of the results, we propose a new mechanism, slow intersystem crossing from S1 to T1 without seam of crossing, followed by CH3 dissociation via a TS on T1; this slow pathway will be overtaken by a more efficient S1 pathway for higher energy. This is consistent with the observed long lifetime of the S1 species. Moreover, four channels, including three new ones, were found to regenerate the ground state acetone from the S1 PES, and they all may be involved in the roaming channel that has been proposed recently as a new route of CO generation in a 230 nm photolysis. There are significant differences in MSX structures and energies between the present CASPT2 results and previous CASSCF results.Keywords (keywords): acetone; photodissociation; potential energy surface; seam of crossing; conical intersection; transition state; roaming channel
    Journal of Physical Chemistry Letters 06/2010; 1(12). DOI:10.1021/jz100551y · 6.69 Impact Factor
  • Koichi Ohno, Satoshi Maeda
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    ABSTRACT: Anharmonic downward distortion (ADD) of potential energy surfaces (PES) indicates the direction of reaction routes, and the ADD-following on PES has made it possible to perform global reaction route mapping (GRRM) of a given chemical formula. The GRRM method based on the ADD-following can be applied to real processes of catalytic reactions to elucidate the reaction mechanisms. A systematic analysis of a RuHCl–BINAP-catalyzed asymmetric hydrogenation reaction has given an insight into the role of important adsorption structures and the chirality determining transition state among numerous candidates. Computed reaction profiles for the total catalytic cycles with and without protonation demonstrated significance of the protonation for both high enantioselectivity and high catalytic-activity.
    Journal of Molecular Catalysis A Chemical 06/2010; 324(1):133-140. DOI:10.1016/j.molcata.2010.03.004 · 3.68 Impact Factor
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    ABSTRACT: The conical intersections (CIs) form a (f-2)-dimensional hyperspace on which two diabatic potential energy surfaces (PESs) belonging to the same symmetry cross, where f is the internal degree of freedom. The branching plane (BP) is a (two-dimensional) plane defined by the difference gradient vector (DGV) and the coupling derivative vector (CDV), and on the BP, the degeneracy of the two adiabatic PESs is lifted. The properties of the BP are often used in the exploration of the conical intersection hyperspace, such as determination of the minimum energy CI or the first-order saddle point in CI. Although both DGV and CDV are necessary to construct the BP in general, CDV is not always available depending on ab initio methods and programs. Therefore, we developed an approach for optimizing critical points on the CI hypersurface without CDV by using a BP updating method, which was shown to be accurate and very useful for minimum energy and saddle point optimization and for the minimum energy path following within the CI hypersurface in numerical tests for C6H6 and C5H8N+.
    Journal of Chemical Theory and Computation 04/2010; 6(5). DOI:10.1021/ct1000268 · 5.31 Impact Factor
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    ABSTRACT: Valence ionized states of iron pentacarbonyl Fe(CO)(5) and eta(5)-cyclopentadienyl cobalt dicarbonyl Co(eta(5)-C(5)H(5))(CO)(2) have been studied by ultraviolet photoelectron spectroscopy, two-dimensional Penning ionization electron spectroscopy (2D-PIES), and symmetry-adapted cluster-configuration interaction calculations. Theory provided reliable assignments for the complex ionization spectra of these molecules, which have metal-carbonyl bonds. Theoretical ionization energies agreed well with experimental observations and the calculated wave functions could explain the relative intensities of PIES spectra. The collision-energy dependence of partial ionization cross sections (CEDPICS) was obtained by 2D-PIES. To interpret these CEDPICS, the interaction potentials between the molecules and a Li atom were examined in several coordinates by calculations. The relation between the slope of the CEDPICS and the electronic structure of the ionized states, such as molecular symmetry and the spatial distribution of ionizing orbitals, was analyzed. In Fe(CO)(5), an attractive interaction was obtained for the equatorial CO, while the interaction for the axial CO direction was repulsive. For Co(eta(5)-C(5)H(5))(CO)(2), the interaction potential in the direction of both Co-C-O and Co-Cp ring was attractive. These anisotropic interactions and ionizing orbital distributions consistently explain the relative slopes of the CEDPICS.
    The Journal of Chemical Physics 02/2010; 132(8):084302. DOI:10.1063/1.3319778 · 3.12 Impact Factor

Publication Stats

3k Citations
630.13 Total Impact Points

Institutions

  • 1995–2015
    • Tohoku University
      • • Department of Chemistry
      • • Graduate School of Science
      Miyagi, Japan
  • 2009–2013
    • Toyota Physical and Chemical Institute
      Seto, Aichi, Japan
  • 1980–2002
    • The University of Tokyo
      • Department of Chemistry
      Edo, Tōkyō, Japan
  • 1998
    • Wakayama University
      • Department of Material Science and Chemistry
      Wakayama, Wakayama, Japan
  • 1991
    • Toho University
      • Department of Biomolecular Science
      Edo, Tōkyō, Japan