Koichi Ohno

Hokkaido University, Sapporo-shi, Hokkaido, Japan

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Publications (219)379.52 Total impact

  • [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). · 5.83 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 transition from the π orbital of the Si=C double bond to the π* orbital of the anthryl moiety. Relatively high-lying π(Si=C) orbital of the 3-silylene-2-silaaziridine moiety and low-lying π* orbital of the anthryl group would be responsible for the distinct ICT band.
    Journal of the American Chemical Society 07/2013; · 10.68 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; · 2.77 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; · 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 01/2012; 2012.
  • 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 01/2011; 503(4):322-326. · 2.15 Impact Factor
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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. · 2.77 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.
    Journal of Physical Chemistry C - J PHYS CHEM C. 08/2010;
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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.
  • 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.
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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
    The Journal of Physical Chemistry Letters. 06/2010; 1(12).
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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). · 5.39 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. · 3.12 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 - J MOL CATAL A-CHEM. 01/2010; 324(1):133-140.
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    ABSTRACT: Four isolable dialkylsilanimines RH2SiNR (R = CH2Ph (5a), Ph (5b), 1-adamantyl (5c) and SiMe3 (5d), where RH2 = 1,1,4,4-tetrakis(trimethylsilyl)butane-1,4-diyl) were synthesized as air-sensitive crystals by the reaction of isolable dialkylsilylene 4 with the corresponding azides. X-ray analysis shows that 5a–5d are base-free silanimines and 5a and 5b have a remarkable bent SiN–R structure, while 5c and 5d have an almost linear structure. Distinct π(SiN)→π*(SiN) and n(N)→π*(SiN) transition bands of silicon–nitrogen double bonds were observed for 5a–5d in hexane. A mechanism for the formation of silanimine from the reaction of silylene and azide is discussed using theoretical calculations with the GRRM method for model reactions.
    New Journal of Chemistry 01/2010; 34(8). · 2.97 Impact Factor
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    ABSTRACT: We have investigated adsorption of molecules with hydroxyl group, ROH, on sodium halide cluster ions, Na(n)X(n-1)(+) (X = F and I, n = 10-17) by mass spectrometry and by theoretical calculations. From analysis of the cluster ion intensities, the adsorption of one water molecule (R = H) is most efficient for Na(13)X(12)(+), whose structure has a NaX defect from a 3 x 3 x 3 cubic structure of n = 14. This result suggests that the defect has an important role in the adsorption reaction. However, it is also found that the reactivity diminishes with increasing bulk size of the R group from H to CH(3), (CH(3))(2)CH, and (CH(3))(3)C. These results imply that the adsorption reactivity is dominated by steric hindrance; the smaller molecules are adsorbed inside the basket structures of Na(13)X(12)(+). Reactivity dependence on the basket size is also discussed by comparing the results of Na(n)F(n-1)(+) and Na(n)I(n-1)(+).
    The Journal of Physical Chemistry A 12/2009; 114(3):1432-6. · 2.77 Impact Factor
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    ABSTRACT: The global reaction route mapping (GRRM) method enabled an automated and a systematic search for routes of chemical reactions on a potential energy surface based on the anharmonic downward distortion following (ADDF) approach [Chem. Phys. Lett. 2004, 384, 277]. On the other hand, the microiteration technique [Mol. Phys. 2006, 104, 701] has been developed for full optimizations of transition state (TS) structures for reactions/transformations in large flexible molecular systems and successfully used in ONIOM(QM:MM) calculations. In the present paper, combining the GRRM method with the microiteration technique, we developed a microiteration-ADDF (μ-ADDF) method for automated and systematic TS exploration of large flexible molecular systems. We showed that the method works well with two test systems, (H2CO)(H2O)100 and Si6(C12H17)6, in the ONIOM(QM:MM) framework. It is noted that the present μ-ADDF method can be used for pure quantum mechanics (QM) or molecular mechanics (MM) systems (without ONIOM) and has been tested successfully in C6H10O pure QM calculations.
    Journal of Chemical Theory and Computation - J CHEM THEORY COMPUT. 10/2009; 5(10).
  • Naoki Kishimoto, Koichi Ohno
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    ABSTRACT: Penning ionization of dibenzenechromium with He*(23S) metastable atoms was observed by collision-energy-resolved two-dimensional electron spectroscopy. Collision energy dependence of partial ionization cross sections (CEDPICS) indicates that attractive interaction around the benzene rings (Bz) results in negative slope of CEDPICS for ionization from valence πBz orbtials. Negative CEDPICS of bands 1 and 2 was ascribed to strong electron correlation effects in mixing configurations of direct ionization from metal d orbitals and shake-up excitation as shown by CI calculation. Repulsive interaction was also found around the sCH bonds and the Cr atom.
    Journal of Physics Conference Series 10/2009; 185(1):012020.
  • Yoshihiro Yamakita, Koichi Ohno
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    ABSTRACT: The phonon dispersion curves are presented for a carbon nanoribbon, polyacene. Restricted and unrestricted density functional calculations for [n]oligoacenes (n = 10 and 15) predict different spin distributions in the singlet electronic state. The unrestricted states involve spin-localized, singly-occupied orbitals. Bond alternations, infrared activities and phonon dispersions are studied on the basis of these closed-shell and open-shell states, respectively. Vibronic coupling in S0←S1 transitions are investigated using an efficient quantum chemical model (MO/8 model). Franck-Condon and vibronic coupling transitions in oligoacenes are found to be activated commonly, and the vibronic activities are assigned to the same phonon dispersion branches of polyacene.
    Journal of Physics Conference Series 10/2009; 185(1):012055.
  • Naoki Kishimoto, Koichi Ohno
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    ABSTRACT: Outer valence ionic states of Cr(CO)(6) and (eta(5)-C(5)H(5))Co(CO)(2) were investigated by means of Penning ionization electron spectroscopy (PIES) upon collision with metastable He*(2(3)S) excited atoms as well as high-level ab initio molecular orbital calculations taking electron correlation effects into consideration. By the 2D measurement combining the collision-energy-resolved technique of the metastable atomic beam and electron spectroscopy, ionic-state-resolved measurement of collision energy dependence of partial ionization cross sections (CEDPICS) was carried out. Because partial Penning ionization cross sections can be connected to the spatial extent of corresponding molecular orbitals (MOs) outside the boundary surface of colliding He* atoms, different slopes of CEDPICS were related to anisotropic interaction around the MO region. The observed CEDPICS and PIES band intensity were consistent with the order of calculated ionic states.
    The Journal of Physical Chemistry A 09/2009; 113(52):14559-64. · 2.77 Impact Factor

Publication Stats

744 Citations
379.52 Total Impact Points


  • 2013
    • Hokkaido University
      • Department of Chemistry
      Sapporo-shi, Hokkaido, Japan
  • 2010–2013
    • Toyota Physical and Chemical Institute
      Seto, Aichi, Japan
    • Institute for Molecular Science
      Okazaki, Aichi, Japan
  • 1995–2013
    • Tohoku University
      • • Department of Chemistry
      • • Graduate School of Science
      Sendai, Kagoshima-ken, Japan
  • 2009
    • Emory University
      • Cherry L. Emerson Center for Scientific Computation
      Atlanta, GA, United States
  • 1980–2004
    • The University of Tokyo
      • • College of Art and Science & Graduate School of Arts and Sciences
      • • Department of Chemistry
      • • Department of Chemistry and Biotechnology
      Tokyo, Tokyo-to, Japan