Tetsuya Taketsugu

Kyoto University, Kioto, Kyōto, Japan

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Publications (143)481.37 Total impact

  • Keisuke Niimi, Tetsuya Taketsugu, Akira Nakayama
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    ABSTRACT: The matrix shifts of the H-Xe stretching frequency of noble-gas hydrides, HXeCCH, HXeBr, and HXeI in various noble-gas matrices (in Ne, Ar, Kr, and Xe matrices) are investigated via the hybrid quantum-classical simulations. The order of the H-Xe stretching frequencies is found to be ν(gas) < ν(Ne) < ν(Xe) < ν(Kr) < ν(Ar) for HXeCCH and HXeBr, while it is ν(gas) < ν(Ne) < ν(Xe) < ν(Ar) < ν(Kr) for HXeI. This order is anomalous with respect to the matrix dielectric constants, and the calculated results reproduce the experimentally observed shifts quite successfully. We also find that the matrix shifts from the gas-phase values are Δν(HXeCCH) ≈ Δν(HXeCl) < Δν(HXeBr) < Δν(HXeI) in the same noble-gas matrix environments, which implies that the weakly bound molecules exhibit large matrix shifts. The local trapping site is analyzed in detail, and it is shown that a realistic modeling of the surrounding matrix environments is essential to describe the unusual matrix shifts accurately.
    Physical chemistry chemical physics : PCCP. 02/2015;
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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; · 11.44 Impact Factor
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    ABSTRACT: Experimental and theoretical studies of HXeI and HXeH molecules in Ar, Kr, and Xe matrices are presented. HXeI exhibits the H-Xe stretching bands at 1238.0 and 1239.0 cm(-1) in Ar and Kr matrices, respectively, that are blue-shifted from the HXeI band observed in a Xe matrix (1193 cm(-1)) by 45 and 46 cm(-1). These shifts are larger than those observed previously for HXeCl (27 and 16 cm(-1)) and HXeBr (37 and 23 cm(-1)); thus, the matrix effect is stronger for less stable molecules. The results for HXeI are qualitatively different from all previous results on noble-gas hydrides with respect to the frequency order between Ar and Kr matrices. For previously studied HXeCl, HXeBr, and HXeCCH, the H-Xe stretching frequency is reliably (by >10 cm(-1)) higher in an Ar matrix than in a Kr matrix. In contrast, the H-Xe stretching frequency of HXeI in an Ar matrix is slightly lower than that in a Kr matrix. HXeH absorbs in Ar and Kr matrices at 1203.2 and 1192.1 cm(-1) (the stronger band for a Kr matrix), respectively. These bands are blue-shifted from the stronger band of HXeH in a Xe matrix (1166 cm(-1)) by 37 and 26 cm(-1), and this frequency order is the same as observed for HXeCl, HXeBr, and HXeCCH but different from HXeI. The present hybrid quantum-classical simulations successfully describe the main experimental findings. For HXeI in the 〈110〉 (double substitution) site, the order of the H-Xe stretching frequencies (ν(Xe) < ν(Ar) < ν(Kr)) is in accord with the experimental observations, and also the frequency shifts in Ar and Kr matrices from a Xe matrix are well predicted (30 and 34 cm(-1)). Both in the theory and experiment, the order of the H-Xe stretching frequencies differs from the case of HXeCl, which suggests the adequate theoretical description of the matrix effect. For HXeH in the 〈100〉 (single substitution) site, the order of the frequencies is ν(Xe) < ν(Kr) < ν(Ar), which also agrees with the experiments. The calculated frequency shifts for HXeH in Ar and Kr matrices with respect to a Xe matrix (36 and 23 cm(-1)) are in a good agreement with the experiments. The present calculations predict an increase of the H-Xe stretching frequencies in the noble-gas matrices with respect to vacuum.
    The Journal of Chemical Physics 02/2015; 142(5):054305. · 3.12 Impact Factor
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    ABSTRACT: This work present results of a systematic investigation of adsorption and dissociation of H2 on the neutral, positively, and negatively charged gold clusters Aunq (n = 2–11; q = 0, ±1) using the global reaction route mapping (GRRM) technique combined with the anharmonic downward distortion following (ADDF) and the artificial force-induced reaction (AFIR) methods. An exhaustive search for H2 dissociation pathways is performed not only on the most stable cluster structures but also on the large number of low-energy isomers, allowing structural transformations between them. The present strategy can automatically identify the structure-dependent lowest transition states (TS) for H2 dissociation with a systematic procedure in the regime of the structural fluxionality of gold clusters at finite temperature. Temperature effects, cluster isomerization, and influence of the charge state of gold clusters on H2 adsorption and dissociation are studied. It is demonstrated that the most stable structures of the gold clusters are not always highly reactive, and an ensemble of isomeric structures must be taken into account for adequate description of the reaction rates at finite temperatures. The proposed approach can serve as a promising tool for a systematic analysis and prediction of reactivity of small metal clusters.
    The Journal of Physical Chemistry C 01/2015; · 4.84 Impact Factor
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    ABSTRACT: To expand the originally developed fluorescent 1,3a,6a-triazapentalenes as fluorescent labeling reagents, the fluorescence wavelength of 1,3a,6a-triazapentalene was extended to the red color region. Based on the noteworthy correlation of the fluorescence wavelength with the inductive effect of the 2-substituent, further electron-deficient 2-(2-cyano-4-methoxycarbonylphenyl)-1,3a,6a-triazapentalene and 2-(2,6-dicyano-4-methoxycarbonylphenyl)-1,3a,6a-triazapentalene were synthesized. The former exhibited yellow and the latter exhibited red fluorescence, and both compounds exhibited large Stokes shifts, and the 1,3a,6a-triazapentalene system enabled the same fluorescent chromophore to cover the entire region of visible wavelengths. The potential applications of the 1,3a,6a-triazapentalenes as fluorescent probes in the fields of the life sciences were investigated, and the 1,3a,6a-triazapentalene system was clearly proven to be useful as a fluorescent reagent for live cell imaging. Quantum chemical calculations were performed to investigate the optical properties of 1,3a,6a-triazapentalenes. These calculations revealed that the excitation involves a significant charge-transfer from the 1,3a,6a-triazapentalene skeleton to the 2-substituent. The calculated absorption and fluorescence wavelengths showed a good correlation with the experimental ones, and thus the system would enable the theoretical design of substituents with the desired optical properties.
    Chemical Science 10/2014; · 8.60 Impact Factor
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    ABSTRACT: Locating accessible conical intersections (CIs), especially minimum energy CI (MECI) structures, near the Franck-Condon (FC) region is one of the most important tasks in theoretical analyses of photoreactions. Many MECIs may exist around a FC point in molecules with many vibrational degrees of freedom. Usually, MECIs are optimized one by one starting from arbitrary chosen initial structures. In order to eliminate the arbitrariness, we have developed automated MECI search methods. In this paper, a new approach is described. It combines the seam model function approach with the recently proposed single-component artificial force induced reaction method. Starting from a FC point, the present method finds MECIs systematically. It requires neither a Hessian nor a derivative coupling vector. In an example of the automated search, the spin-flip TDDFT was employed as an efficient electronic structure calculation method, which, together with an automated algorithm to recognize proper electronic states, allowed for evaluation of energy and gradient in a black-box fashion. The present approach was tested with trans- and cis-1,3-butadiene, thymine, and coumarin molecules. The usefulness of the present approach was demonstrated by comparing obtained MECIs with those in the literature. It is hoped that the present technique will be useful in exploration of unknown photoreaction pathways.
    The Journal of Physical Chemistry A 09/2014; · 2.78 Impact Factor
  • Akira Nakayama, Shohei Yamazaki, Tetsuya Taketsugu
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    ABSTRACT: The nonradiative deactivation pathways of cytosine derivatives (cytosine, 5-fluorocytosine, 5-methylcytosine, and 1-methycytosine) and their tautomers are investigated by quantum chemical calculations, and the substituent effects on the deactivation process are examined. The MS-CASPT2 method is employed in the excited-state geometry optimization and also in the search for conical intersection points, and the potential energy profiles connecting the Franck-Condon point, excited-state minimum energy structures, and the conical intersection points are investigated. Our calculated vertical and adiabatic excitation energies are in quite good agreement with experimental results, and the relative barrier heights leading to the conical intersections are correlated with the experimentally observed excite-state lifetimes, where the calculated barrier heights are in the order of cytosine < 5-methylcytosine < 5-fluorocytosine.
    The Journal of Physical Chemistry A 09/2014; · 2.78 Impact Factor
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    ABSTRACT: On-the-fly dynamics simulations were carried out using spin-flip time dependent density functional theory (SF-TDDFT) to examine the photoisomerization and photocyclization mechanisms of cis-stilbene following excitation to the ππ* state. A state tracking method was devised to follow the target state among nearly degenerate electronic states during the dynamics simulations. The steepest descent path from the Franck-Condon structure of cis-stilbene in the ππ* state is shown to reach the S1-minimum of 4,4-dihydrophenanthrene (DHP) via a cis-stilbene-like structure (referred to as (S1)cis-min) on a very flat region of the S1-potential energy surface. From the dynamics simulations, the branching ratio of the photoisomerization is calculated as trans: DHP = 35: 13, in very good agreement with the experimental data, trans: DHP = 35: 10. The discrepancy between the steepest descent pathway and the significant trans-stilbene presence in the branching ratio observed experimentally and herein computationally is clarified from an analysis of geometrical features along the reaction pathway, as well as the low barrier of 0.1 eV for the pathway from (S1)cis-min to the twisted pyramidal structure on the S1-potential energy surface. It is concluded that ππ*-excited cis-stilbene propagates primarily toward the twisted structural region due to dynamic effects, with partial branching to the DHP structural region via the flat-surface region around (S1)cis-min.
    The Journal of Physical Chemistry A 09/2014; · 2.78 Impact Factor
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    ABSTRACT: The intrinsic reaction coordinate (IRC) approach has been used extensively in quantum chemical analysis and prediction of the mechanism of chemical reactions. The IRC gives a unique connection from a given transition structure to local minima of the reactant and product sides. This allows for easy understanding of complicated multistep mechanisms as a set of simple elementary reaction steps. In this article, three topics concerning the IRC approach are discussed. In the first topic, the first ab initio study of the IRC and a recent development of an IRC calculation algorithm for enzyme reactions are introduced. In the second topic, cases are presented in which dynamical trajectories bifurcate and corresponding IRC connections can be inaccurate. In the third topic, a recent development of an automated reaction path search method and its application to systematic construction of IRC networks are described. Finally, combining these three topics, future perspectives are discussed. © 2014 Wiley Periodicals, Inc.
    International Journal of Quantum Chemistry 09/2014; · 1.17 Impact Factor
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    ABSTRACT: Femtosecond relaxation and picosecond photodissociation dynamics of 1,3-butadiene were investigated by time-resolved photoelectron spectroscopy with high harmonics pulses, probing the deeper molecular orbitals which are sensitive to the molecular structure.
    CLEO: QELS_Fundamental Science; 06/2014
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    ABSTRACT: In trans-1,3-butadiene, the ultrafast relaxation from the doubly excited state 21Ag and the corresponding recovery of the ground state 11Ag were observed simultaneously for the first time by time-resolved photoelectron spectroscopy (TRPES) using 29.5 eV high harmonic pulses. The fast recovery of 11Ag shows that the following dissociation upon photoexcitation takes place after returning to the ground state. At 427 fs after photoexcitation, only the ionization energy from the C═C σ bond was found to remain shifted. Accompanying theoretical calculations with an assumption of Koopmans’ theorem show that the ionization energy of the C═C σ bond is modulated by vibrational excitation of the antisymmetric C═C stretching mode. TRPES by high harmonics can probe the changes in the molecular structure sensitively.
    Journal of Physical Chemistry Letters 05/2014; 5(10):1760–1765. · 6.69 Impact Factor
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    ABSTRACT: Boron nitride (BN), which is an insulator with a wide band gap, supported on Au is theoretically suggested and experimentally proved to act as an electrocatalyst for oxygen reduction reaction (ORR). Density-functional theory calculations show that the band gap of a free h-BN monolayer is 4.6 eV but a slight protrusion of the unoccupied BN states toward the Fermi level is observed if BN is supported on Au(111) due to the BN-Au interaction. A theoretically predicted metastable configuration of O2 on h-BN/Au(111), which can serve as precursors for ORR, and free energy diagrams for ORR on h-BN/Au(111) via two- and four-electron pathways show that ORR to H2O2 is possible at this electrode. It is experimentally proved that overpotential for ORR at the gold electrode is significantly reduced by depositing BN nanosheets. No such effect is observed at the glassy carbon electrode, demonstrating the importance of BN-substrate interaction for h-BN to act as the ORR electrocatalyst. A possible role of the edge of the BN islands for ORR is also discussed.
    Journal of the American Chemical Society 04/2014; · 11.44 Impact Factor
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    ABSTRACT: Main-group-element catalysts are a desirable alternative to transition-metal catalysts because of natural abundance and cost. However, the examples are very limited. Catalytic cycles involving a redox process and E-ligand cooperation (E=main-group element), which are often found in catalytic cycles of transition-metal catalysts, have not been reported. Herein theoretical investigations of a catalytic hydrogenation of azobenzene with ammonia-borane using a trivalent phosphorus compound, which was experimentally proposed to occur through P(III) /P(V) redox processes via an unusual pentavalent dihydridophosphorane, were performed. DFT and ONIOM(CCSD(T):MP2) calculations disclosed that this catalytic reaction occurs through a P-O cooperation mechanism, which resembles the metal-ligand cooperation mechanism of transition-metal catalysts.
    Angewandte Chemie International Edition 03/2014; · 11.34 Impact Factor
  • Min Gao, Andrey Lyalin, Satoshi Maeda, Tetsuya Taketsugu
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    ABSTRACT: A new theoretical approach to find metal-cluster-catalyzed single bond activation pathways is introduced. The proposed approach combines two automated reaction path search techniques: the anharmonic downward distortion following (ADDF) and the artificial force induced reaction (AFIR) methods, developed in our previous works [Maeda, S.; Ohno, K.; Morokuma, K. Phys. Chem. Chem. Phys. 2013, 15, 3683−3701]. A simple model reaction of the H−H bond activation catalyzed by Aun (n = 7, 8) clusters is considered as an example. We have automatically found 33 and 20 transition-state (TS) structures for H2 dissociation on Au7 and Au8 clusters, respectively, and successfully identified the best dissociation pathways with the lowest barrier. Systematic analysis of the structure-dependent reactivity of small gold clusters is performed. It is demonstrated that the most stable structures of the gold clusters are not always highly reactive and several isomeric structures must be taken into account for adequate description of the reaction rates at finite temperatures. The proposed approach can serve as a promising tool for investigation of the chemical reactions catalyzed by small metal clusters.
    Journal of Chemical Theory and Computation 03/2014; 10:1623-1630. · 5.39 Impact Factor
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    ABSTRACT: Photophysical behavior of three lowest-energy tautomers of uric acid and seven most stable isomers of uric acid monohydrate is comprehensively studied by ab initio calculations. Ground-state energies are calculated with the CCSD(T) method, while excitation and ionization energies as well as excited-state potential-energy profiles of photoinduced processes are calculated with the CC2 method. For the (1)ππ* state, it is found that excitation energy of the monohydrate cluster is significantly lower than that of isolated uric acid when the water molecule is hydrogen-bonded at a specific carbonyl group. The calculated excited-state potential-energy profiles suggest that some monohydrate isomers can undergo a migration of the water molecule from one site to another site in the (1)ππ* state with a small energy barrier. It is also found for both uric acid and its monohydrate that nonradiative decay via the NH bond dissociation in the (1)πσ* state is likely to occur at higher excitation energies. Based on the computational results, possible mechanisms for the absence of specific isomers of uric acid monohydrate from the resonant two-photon ionization spectrum are discussed.
    The Journal of Physical Chemistry A 01/2014; · 2.77 Impact Factor
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    ABSTRACT: Ultrafast and photodissociation dynamics of a cumulated dine molecule, 1,2-butadiene, were investigated by time-resolved photoelectron spectroscopy using a high harmonic. In contrast with 1,3-butadiene, coherent oscillation by stimulated Raman process was observed prior to photodissociation.
    International Conference on Ultrafast Phenomena; 01/2014
  • Keisuke Niimi, Akira Nakayama, Yuriko Ono, Tetsuya Taketsugu
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    ABSTRACT: The hybrid quantum-classical simulations are performed to investigate the unusual vibrational spectral shifts of a noble-gas hydride HXeCl in matrix environments (in Ne, Ar, Kr, and Xe matrices). The high-level ab initio calculations employing the CCSD(T) method are performed to construct interaction potential energy surfaces between HXeCl and noble-gas atoms (Ne, Ar, Kr, and Xe). The configurations of noble-gas atoms are sampled by the Monte Carlo simulations and the vibrational levels of HXeCl in the presence of the surrounding noble-gas atoms are solved by the DVR approach. It is found that the H-Xe stretching frequencies are blue-shifted from the isolated gas-phase value in all matrix environments and that the relative blue shifts are in good agreement with the experimental results (Ne < Xe < Kr), demonstrating that the explicit treatment of matrix environments around HXeCl is essential to reproduce the observed unusual vibrational shifts.
    The Journal of Physical Chemistry A 12/2013; · 2.77 Impact Factor
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    ABSTRACT: On-the-fly excited-state quantum mechanics∕molecular mechanics molecular dynamics (QM∕MM-MD) simulations of thymine in aqueous solution are performed to investigate the role of solvent water molecules on the nonradiative deactivation process. The complete active space second-order perturbation theory (CASPT2) method is employed for a thymine molecule as the QM part in order to provide a reliable description of the excited-state potential energies. It is found that, in addition to the previously reported deactivation pathway involving the twisting of the C-C double bond in the pyrimidine ring, another efficient deactivation pathway leading to conical intersections that accompanies the out-of-plane displacement of the carbonyl group is observed in aqueous solution. Decay through this pathway is not observed in the gas phase simulations, and our analysis indicates that the hydrogen bonds with solvent water molecules play a key role in stabilizing the potential energies of thymine in this additional decay pathway.
    The Journal of Chemical Physics 12/2013; 139(21):214304. · 3.12 Impact Factor
  • Satoshi Maeda, Tetsuya Taketsugu, Keiji Morokuma
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    ABSTRACT: Finding all required transition state (TS) structures is an important but hard task in theoretical study of complex reaction mechanisms. In the present article, an efficient automated TS search method, artificial force induced reaction (AFIR), was extended to intramolecular reactions. The AFIR method has been developed for intermolecular associative pathways between two or more reactants. Although it has also been applied to intramolecular reactions by dividing molecules manually into fragments, the fragmentation scheme was not automated. In this work, we propose an automated fragmentation scheme. Using this fragmentation scheme and the AFIR method, a fully automated search algorithm for intramolecular pathways is introduced. This version for intramolecular reactions is called single-component AFIR (SC-AFIR), to distinguish it from multicomponent AFIR for intermolecular reactions. SC-AFIR was tested with two reactions, the Claisen rearrangement and the first step of cobalt-catalyzed hydroformylation, and successfully located all important pathways reported in the literature. © 2013 Wiley Periodicals, Inc.
    Journal of Computational Chemistry 11/2013; 35(2). · 3.60 Impact Factor
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    Ryohei Uematsu, Satoshi Maeda, Tetsuya Taketsugu
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    ABSTRACT: A systematic search for reaction pathways for the vinylogous Mannich-type reaction was performed by the artificial force induced reaction method. This reaction affords δ-amino-γ-butenolide in one pot by mixing 2-trimethylsiloxyfuran, imine, and water under solvent-free conditions. Surprisingly, the search identified as many as five working pathways. Among them, two concertedly produce anti and syn isomers of the product. Another two give an intermediate, which is a regioisomer of the main product. This intermediate can undergo a retro-Mannich reaction to give a pair of intermediates: an imine and 2-furanol. The remaining pathway directly generates this intermediate pair. The imine and 2-furanol easily react with each other to afford the product. Thus, all of these stepwise pathways finally converge to give the main product. The rate-determining step of all five (two concerted and three stepwise) pathways have a common mechanism: concerted SiO bond formation through the nucleophilic attack of a water molecule on the silicon atom followed by proton transfer from the water molecule to the imine. Therefore, these five pathways have comparable barriers and compete with each other.
    Chemistry - An Asian Journal 10/2013; · 4.57 Impact Factor

Publication Stats

2k Citations
481.37 Total Impact Points


  • 2014
    • Kyoto University
      Kioto, Kyōto, Japan
  • 2005–2014
    • Hokkaido University
      • • Division of Chemistry
      • • Graduate School of Science
      • • Department of Chemistry
      Sapporo, Hokkaidō, Japan
  • 2008–2012
    • RIKEN
      • Nuclear Spectroscopy Laboratory
      Wako, Saitama-ken, Japan
  • 2011
    • Minoufiya University
      • Department of Chemistry
      Shibīn al Kawm, Muhafazat al Minufiyah, Egypt
  • 1999–2008
    • Ochanomizu University
      • • Department of Chemistry
      • • Graduate School of Humanities and Sciences
      Tōkyō, Japan
  • 2004
    • Institute for Molecular Science
      Okazaki, Aichi, Japan
    • Tokyo Institute of Technology
      • Research Laboratory for Nuclear Reactors
      Tokyo, Tokyo-to, Japan
  • 1993–2004
    • The University of Tokyo
      • • Faculty & Graduate School of Engineering
      • • Department of Applied Chemistry
      Tokyo, Tokyo-to, Japan
  • 2001–2002
    • University of Cambridge
      • Department of Chemistry
      Cambridge, England, United Kingdom
  • 1996
    • Iowa State University
      Ames, Iowa, United States