Toshikazu Takada

Abinitio SCF‐CI calculation on free base porphin and chlorin; theoretical analysis on intensities of the absorption spectra

Ab initio self‐consistent field and configuration interaction (SCF‐CI) calculations with a minimal basis set are carried out on a few lower π→π* states of free base porphin and free base chlorin. Excitation energies and oscillator strength of these states are calculated and are compared with observed values. For the two lowest states of porphin and chlorin, the calculated excitation energies and oscillator strength are in good agreement with the observed ones. In particular, a characteristic of chlorin spectra is reproduced by the calculation. Namely, the oscillator strength of the lowest transition is several times larger than that of porphin but the oscillator strength of the second transition is similar to that of porphin. Such differences of the oscillator strength between chlorin and porphin are explained by an interchange of the order of two highest occupied orbitals and that of the two lowest unoccupied orbitals. Those differences are caused by a change of orbital shapes of chlorin due to the addit...

Abinitio SCF CI calculations on the ground and π–π* excited states of the pyrrole molecule and its positive ion

Ab initio SCF π‐electron CI calculations are carried out on the ground and lower π–π* excited states of pyrrole and its positive ion. The four singlet states found at 5.9, 6.8, 7.2, and 7.4 eV by experiment are tentatively assigned as the 1B2, 1A1, 1B2, and 1A1 states, respectively. The calculated excitation energies for these four states are 6.0, 6.5, 7.1, and 7.3 eV, respectively. The first excited 1A1 state is a valence type state, whereas the other three states are Rydberg type states. The lowest excited state found at 4.35 eV by experiment is assigned as the 3B2 state, whose calculated excitation energy is 4.27 eV. The three lowest excited states of the positive ion due to π‐electron ionization are also investigated. The calculated ionization potentials are 8.10 (2A2), 8.94 (2B1), and 13.33 eV (2B1). They are in good agreement with experimental values of 8.21, 9.20, and 13.0 eV. The lowest two states are represented by la2→∞ and 2b1 →∞, respectively, whereas the second 2B1 state is a mixture of three...

Silacyclopentadienylidene, the first silylene incorporated in a silole ring

Silacyclopentadienylidene 1 was generated photochemically using 7-silanorbornadiene and norbornene precursors and observed in frozen hydrocarbon matrices at 77 K.

A simple method to eliminate linearly dependent AO integrals in ab initio LCAO MO calculations by taking advantage of shell structure

A new method to eliminate linearly dependent two electron integrals in an AO basis is proposed. In the conventional method, the number of computer operations to make the list of independent integrals is proportional to the number of two electron integrals. It is proportional to the number of overlap charges in the present method. Thus, the computer time required is negligible in comparison with the conventional method. Results of actual computations using, the present method are reported for naphthalene (C10H8), cyclobutane (C4H8) and NiF6.