Hiroshi Morita

Theoretical study on the photostimulated desorption of CO from a Pt surface

Photostimulated desorptions (PSD’s) of CO, CO+, and CO− from a Pt surface are studied theoretically using Pt2–CO model cluster including image force correction. Calculations are performed by the single excitation configuration interaction and the symmetry adapted cluster (SAC)/SAC‐CI methods. The PSD’s of the ground state CO occur as the Menzel–Gomer–Redhead (MGR) process and those of CO+ (n cation) and excited (n→π*) CO* through the modified MGR process in which the upper repulsive potential curves are nonadiabatic; the process proceeds through a sequence of nonadiabatic transitions between the similar pertinent states embedded in the metal excited bands. The excited states as the desorption channels are characterized by the excitations from the Pt–CO bonding orbitals to the antibonding MO’s: metal‐adsorbate chemical bond cleavage by photons which leads to a repulsive potential is essential for the PSD. The electrostatic image force interaction plays only a minor role and the present result does not support the Antoniewicz model. The calculated excitation‐energy thresholds for the CO, CO+, and CO* desorptions are 1.6∼2.6, 11.3, and 11.3–12.7 eV, respectively, which explains the energy thresholds and the fluence dependencies of the incident laser in the PSD experiments. On the other hand, the PSD giving CO− would occur with the energy range of 6.2–8.2 eV, one to two photon energy of the 193 nm (6.4 eV) laser. Since the upper nonadiabatic potential curves have shallow minima, in this case, the lifetime of the CO− species would be larger than those of the CO+ and CO* species. The present study clarifies the electronic structures of the desorbed CO+, CO−, and CO* species, which have not been identified experimentally.

Dipped adcluster model and SAC-CI method applied to harpooning, chemiluminescence and electron emission in halogen chemisorption on alkali metal surface

Abstract The methodology of our laboratory, the dipped adcluster model (DAM) and the symmetry adapted cluster configuration interaction (SAC-CI) method, are briefly reviewed and successfully applied to the electron transfer processes, harpooning, surface chemiluminescence, and surface electron emission, in the course of the chemisorption of halogen molecule on an alkali metal surface. This success encourages us to apply our methodology to surface photochemistry.

Synthesis of biotin-vitamers from pimelic acid and coenzyme A by cell-free extracts of various bacteria

Abstract The activity of cell-free extracts to synthesize pimelyl-CoA from pimelic acid and CoA was indirectly determined in a reaction coupled with the 7-keto-8-aminopelargonic acid synthetase system, which is required for the conversion of pimelyl-CoA to 7-keto-8-aminopelargonic acid, and by measuring the amount of 7-keto-8-aminopelargonic acid formed by microbiological assay. Using this assay method, biotin-vitamers were synthesized from pimelic acid, CoA, ATP and Mg2+, instead of from pimelyl CoA by cell-free extracts of various bacteria. The vitamers synthesized by cell-free extracts of Bacillus megaterium and Bacillus sphaericus were identified as 7-keto-8-aminopelargonic acid and 7,8-diaminopelargonic acid, respectively.

ELECTRONIC STRUCTURES OF THE GROUND AND EXCITED STATES OF MO(CO)6:SAC-CI CALCULATION AND FROZEN ORBITAL ANALYSIS

The symmetry adapted cluster (SAC) and symmetry adapted cluster–configuration interaction (SAC-CI) many body theories have been applied to calculate ground- and excited-state energies, and oscillator strengths of Mo(CO)6. The experimental spectrum of Mo(CO)6 is well reproduced by the present study, which is the first ab initio study of the excited states including electron correlations. The lower excited states are characterized as the metal-to-ligand chargetransfer (MLCT), ligand field transition (LFT) and Rydberg excitations. The LFT states are calculated to be much higher than the experimentally expected values. A new assignment based on the present calculations is proposed. The frozen orbital analysis (FZOA) method is applied to rationalize clearly the physical basis of the ordering of the excited states. This analysis is shown to be useful for understanding the excitation levels.