1. Current Research and Principal Research Interests
The first major area of our research is related to the understanding of chemical reaction mechanisms on ground and excited states of molecules. Examples include some isomerization reactions of five-membered compounds. This major area involves a nonadiabatic process caused by the crossing of several potential energy surfaces. In addition to the studies of this first area, other research deals with non-relativistic phenomena, such as spin-orbit splitting and lifetime of the excited state of molecules. Our last interest is development of a database that includes literatures on theoretical calculations.
Photochemical isomerization of five-membered compounds:
Understanding of the chemical reaction mechanism of many atomic systems is one of the most important subjects in chemistry. Detailed knowledge of micro reaction paths from reactants to products in the chemical reactions and structures of reaction intermediates and transition states on the reaction path are required for this purpose. It is not easy tasks experimentally. Using theoretical methods, however, it is possible to predict the structures of transit species such as intermediates and transition states, and the energetics for very complicated reactions.
Some difficulties can arise in photochemical reactions since many potential surfaces can contribute to the reactions and treatment of several excited states in a well-balanced manner are not easy task if many excited states are considered simultaneously. Photochemical isomerization of five membered heterocyclic compounds has been investigated experimentally. However, details of their reaction mechanisms were not established. We have studied photoisomerization of thiophene, oxazole and iso-oxazole using the ab initio MO CI method. In those projects, we calculated intermediates and transition states of the isomerization and obtained potential energy curves, which provided details of the reaction mechanisms.
The nonadiabatic process is also important for photochemical reactions. Nonadiabatic transitions are expected to predominantly occur at places where two or more potential energy surfaces come close to each other, i.e. avoided crossing, or cross each other, i.e. conical intersection or a crossing seam. This leads to the exact locations of those points on the surfaces being required for understanding of a photochemical process.
Very complicated surface crossings are found at many charge transfer collisions in ion-molecule reactions, and they causes variety of nonadiabatic process. Low-energy dynamics is an interesting example in those collisions. We have studied low-energy charge-transfer collision of the O+ + C2H2 system and obtained the minima of the crossing seam and reaction intermediates. The results indicated that the charge transfer reaction occurs at an early stage via nonadiabatic transition between different spin states.
Spin-orbit interaction can play a key role in a wide range of chemical phenomena. The radiative lifetimes of molecules is one of these and has been studied by many researchers. The radiative lifetimes of electronically excited molecules, however, are generally quite difficult to obtain experimentally if the transition involves a spin-forbidden process. Theoretical methods have been developed which allow such determinations to relatively high accuracy in small molecules that consist of light atoms. The extension of such theoretical methods to a heavier system is desirable, since the spin-orbit interactions that make such transition between states of different multiplicity possible are quite large in heavy atoms. On this basis, we studied radiative lifetimes of excited states of SeO and AsH. To obtain qualitative results, we found that the choice of zero order Hamiltonian was very important. Especially, inclusion of relativistic correction of the kinetic energy part was required to description of the relativistic contraction and expansion of orbitals that has great influences on spin-orbits matrix elements. We proposed a systematic method for treating them. The radiative lifetime of the spin-forbidden process of those states and spin-orbit splitting have been obtained quite satisfactory.
Quantum chemistry literature database:
Literature concerning ab initio computations of atom and molecules published in main journals is contained in this database. The number of literatures exceeds 50,000. It has been utilized by many researches in the fields of physics, chemistry, biology and astronomy.
2. Selected Publications
1. “Resonace Ramman Characterization of Porphycene Anions”, R. M. Gulman, T. Matsushita, S. Neya, N. Funasaki, J. Teraoka, Chem. Phys. Lett., 357, 126-130 (2002)
2. “An ab initio and experimental study of vibrational effects in low energy O+ + C2H2 charge-transfer collisions”, K. Fukuzawa , T. Matsushita, K. Morokuma, D. J. Levandier, Y.-H. Chiu, R, A. Dressler, E. Murad, A. Midey, A. Williams, A. A. Viggiano, J. Chem. Phys., 115, 3184-3194 (2001)
3. "Ab initio MO study of the fragmentation mechanism of the cycloglycylglycine ion in mass spectrometry", T. Takeuchi, N. Higuchi, K Iida Yamamoto, T. Matsushita, K. Nishimoto, J. Mass. Spectrom. Soc. Jpn., 42, 277-286, (1994)
4. "ab initio Study on Effective Exchange Integrals of Binuclear Metal Complexes", M. Fujiwara, T. Matsushita, K. Yamaguchi, T. Fueno, Synth. Met., 1991, 3267-3270 (1991)
5. "ab initio Calculatin of the Radiative Lifetime of the a1Δ and b1Σ+ States in the SeO Molecule", T.
Matsushita, R. Klotz, C. M. Marian, S. D. Peyerimhoff, Mol. Phys., 62, 1385-1402 (1987)
6. "Potential Energy Curves, Zero-Field Splittings, and Radiative Lifetimes for Low-Lying States of AsH", T. Matsushita, C. M. Marian, R. Klotz, S. D. Peyerimhoff, Can. J. Phys., 65, 155-164 (1987)
7. "ab initio caluculation of Isomerization Reaction of Diphosphene1-Sulfide to Thiadiphosphirane", T. Matsushita, K. Hirotsu, T. Higuchi, K. Nishimoto, M. Yoshifuji, K. Shibayama, N. Inamoto, Tetrahedron Lett., 25, 3321-3324 (1984)
8. "Isolation of some Sterically Protected Unsymmetrical Diphosphenes: Nature of Phosphorus-Phosphorus Double Bond", M. Yoshifuji, K. Shibayama, N. Inamoto, T. Matsushita, K. Nishimoto, J. Am. Chem. Soc., 105, 2495-2497 (1983)
9. "An ab initio Calculation on the Proton Transfer in the Benzoic Acid Dimer", S. Nagaoka, N. Hirota, T. Matsushita, K. Nishimoto, Chem. Phys. Lett., 92, 498 (1982)
10. "A Theoretical study on the Photoisomerization of Thiophene", T. Matsushita, Y. Osamura, H. Tanaka, K. Nishimoto, Theor. Chim. Acta, 63, 55-68 (1983)