Kazunari Suzuki

Ab initio calculation of [OH−;e+] system with consideration of electron correlation effect

Ab initio calculations are made to examine theoretically the possibility of stable existence of [OH−;e+] system. Diffuse functions are added to the conventional 6‐31G basis set, considering the wide spread of positron orbital. Moreover, the Mo/ller–Plesset perturbation of the second order is calculated to take the electron correlation into account. These two improvements are found to be very effective for the stable existence of the system. The positron affinity of OH− is computed to be 4.9 eV, and the binding energy of positronium to OH as 0.7 eV which is in good agreement with experimental estimate.

Ab initio intermolecular potential of the ethylene dimer

The intermolecular potential of the ethylene dimer in the ground state has been computed nonempirically with the exchange perturbation theory. The principal terms of interaction energy considered are the Coulombic and exchange energies as the first order ones, then the dispersion energy as the second order one, and other higher terms are neglected. Computations were made exactly without multipole expansion approximation, to the order of the square of intermolecular overlap integrals. Nine orientations of molecules are considered. Three kinds of basis set, i.e., STO‐3G, 4‐31G, and 4‐31G* were employed, and the results were compared to each other and also with those by other authors. The potential minimun was obtained for all orientations against results of other authors, and the most stable one has the slightly shifted parallel structure near to that found in the ethylene crystal.

The PFI-ZEKE photoelectron spectrum of m-fluorophenol and its aqueous complexes: Comparing intermolecular vibrations in rotational isomers

Pulsed field ionization–zero kinetic energy (PFI-ZEKE) photoelectron spectroscopy has been applied to study the cationic ground states of the rotational isomers of m-fluorophenol and its hydrogen-bonded clusters with H2O and D2O. The cis- and trans- monomer isomers are assigned by comparing the observed ionization potentials with values obtained from ab initio calculations (HF/6-31G*). Both monomers display very similar vibrational frequencies, indicating that the geometric structures of the two cations are similar. In contrast, the cis- and trans-aqueous clusters display distinctive intermolecular vibrational frequencies (e.g. the intermolecular stretching vibrations appear at 239 and 228 cm−1 in the cis- and trans-isomers respectively). The origin of the different intermolecular interactions in the isomeric clusters is discussed with reference to the ab initio calculations.

Internal methyl group rotation in o-cresol studied by pulsed field ionization-ZEKE photoelectron spectroscopy

Abstract Pulsed field ionization-ZEKE photoelectron spectroscopy and (1+1) R2PI spectroscopy have been applied to cis - and trans - o -cresol. The internal rotational structure in S 1 has been re-assigned for the cis -isomer, and the potential curve for the internal rotation has been determined. In the PFI-ZEKE spectra recorded via different internal rotational levels in the S 1 state, well-resolved low-frequency bands have been observed. The low-frequency bands are assigned to the internal rotational motion of the methyl group in the cation. Level energies and relative transition intensities are reproduced well by a one-dimensional rotor model with a three-fold axis potential. Potential curves for the internal rotation have been determined for both cis - and trans - o -cresol cations. The barrier height for the internal rotation is different for the two isomers in the cation, while it becomes similar in S 1 . Contributions of steric and electronic factors to the rotational barrier are discussed.

Pulsed field ionization-ZEKE spectroscopy of cresoles and their aqueous complexes: Internal rotation of methyl group and intermolecular vibrations

Pulsed field ionization-ZEKE photoelectron spectroscopy and (1 + 1) R2PI spectroscopy have been applied to the cis- and trans-m-cresol.H2O clusters. The internal rotational structure in the S1 state has been re-assigned, and the potential curve has been determined for the cluster. The PFI-ZEKE spectra of the cis- and trans-isomers show low-frequency bands up to 1000 cm-1 above the adiabatic ionization potential IP0. The low-frequency bands are assigned to the internal rotation of the methyl group, the intermolecular stretching and their combination bands in the m-cresol.H2O cluster cation. Level energies and relative transition intensities are reproduced well by a one-dimensional rotor model with a three-fold axis potential. Potential curves for the internal rotation have been determined for both cis- and trans-isomers of m-cresol.H2O cations. The effect of the cluster formation upon the internal methyl rotation, and the interaction between the methyl rotation and the intermolecular vibration are discussed.

Symmetry‐adapted perturbation theory of the intramonomer correlation effects in intermolecular forces

Molecular interaction energy is studied in terms of the double symmetry‐adapted perturbation theory, taking account of both the electronic exchange between molecules and the intracorrelation fluctuation for individual monomers. The energy is divided into physically meaningful components, such as electrostatic, first‐order exchange, second‐order polarization, and second‐order exchange terms. The algebraic expressions of second‐order component energy terms, especially second‐order exchange ones, are derived for the interaction of two‐electron systems by considering only single‐electronic exchanges between molecules. Our result for the He dimer is compared with that produced when the explicitly correlated Gaussian‐type geminal is employed. The ratio of intracorrelation energy to Hartree–Fock energy in the second‐order exchange is larger than those in the second‐order polarization as well as in the first‐order energies. The interaction energies of the H2 dimer including intracorrelation effect are computed in...

The migration of electrons in disordered solids

The migration of electrons in disordered solids was studied by theoretical analysis and computer simulation. The transfer energy between sites was assumed to be randomly distributed while the site energy to be constant, considering the loose structure of organic solids. The theoretical analysis gives results that the root mean square displacement in initially proportional to time (coherent motion), while after a long time lapse it becomes proportional to the square root of time (diffusive motion). Also, the mean square displacement is found to be proportional to the ratio of the mean value to the width of transfer energy. When the disorder is small the computer simulation gives curves of whose characters are similar to those given theoretically. When the disorder is large, however, the simulation curves show the saturation at long time lapse, that is, the electron is localized in this case. Discussion is made on this point.

Intermolecular interaction energy of CH4 trimer by symmetry-adapted perturbation theory

The interaction energy for the cyclic CH4 trimer is studied in terms of symmetry-adapted perturbation theory. The interaction energy around the van der Waals minimum is dominated by attractive dispersion energy, and the repulsive contribution at the smaller angle region is due to the first-order exchange energy. The total interaction energy is approximated by additive two-body components, because of a mutual cancellation between nonadditive three-body ones.

The Spherical Expansion of H2 Dimer Interaction Energy by Double Symmetry-Adapted Perturbation Theory

Abstract The weak interaction energy of H2 dimer is studied by double symmetry-adapted perturbation theory (SAPT) within second-order of intermolecular and intramonomer perturbation for molecular simulations. The assumed orientations of H2 dimer are linear, parallel, T type and X type. Among four orientations T orientation is the most stable, while linear orientation is the most repulsive. The second-order dispersion energy E disp (2) is the most attractive contribution in all orientations. The interaction energy has the anisotropy, so we expressed our total interaction energy by the spherical expansion to compare with the experimental value. The isotropic interaction energy is about 85% of the experimental value.