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The symmetry-adapted cluster-configuration interaction (SAC/SAC-CI) method is used for studying the chemiluminescence in dimethyl sulfoxide (DMSO) solution and the bioluminescence in the enzyme firefly luciferase (Luc). It is shown that the keto form of OxyL[H.sub.2] has produced red light in chemiluminescence and yellow-green in bioluminescence.

The singlet excited states and doublet ionized/electron-attached states of o-benzoquinone (o-BQ) are analyzed by using the symmetry adapted cluster (SAC)/SAC-configuration interaction (SAC-CI) method. The SAC-CI theoretical spectra have showed that it is essential to take electron correlation into account when describing the singlet and doublet excited states of o-BQ.

Accurate quantum-chemical calculations of the excitation energies and the rotatory strengths of dichalcogens R-Ch-Ch-R (Ch = S, Se, Te) are performed with the symmetry adapted cluster (SAC) and SAC-configuration interaction (CI) methods. The first and second lowest bands have depended on the R-Ch-Ch-R dihedral angle and the calculated trends have agreed with two empirical rules, the [C.sub.2] rule and the quadrant rule.

Molecular structures and excited states of CpM(CO)2 (Cp= eta5-C5H5; M=Rh, Ir) and [C12Rh(CO)2] (super -1) complexes are examined using the B3LYP and the symmetry-adapted cluster (SAC) /SAC-configuration interaction (SAC-Cl) theoretical methods. The wavelength dependence of the quantum efficiencies for the C-H/Si-H bond activations and ligand photosubstitution of CpM(CO)2 can be explained by the existence of the two different types of excited states of CpM(CO)2.

The heterolytic adsorption of H2 on ZnO(1010) surface is examined using an ab initio embedded cluster technique. Results show that the heterolytic adsorption of H2 on ZnO(1010) surface is site-dependent and occurs only on Zn-O ion pairs with low coordination numbers. These include the pairs Zn2c-O3c, Zn3C-O2c and Zn2c-O2c. Computed adsorption heats and vibrational frequencies also showed good agreement with experimental data.

Theoretical investigation of the reaction mechanism and regioselectivity of silastannation of acetylenes with a palladium catalyst shows that electronic effect, steric repulsion and thermodynamic control determine the reactivity and regioselectivity in the reaction. Incorporation of acetylene into the Pd-Sn or Pd-Si bond of the complex is the rate-determining step. The intermediate exhibits an agostic interaction between Pd and H2. Electron density distribution supports the electronic mechanism associated with the reaction.

Excited states of free-base porphyrin isomers, porphycene (Pc), corrphycene (Cor), and hemiporphycene (hPc), are studied by the Symmetry-Adapted Cluster (SAC)/SAC-Configuration Interaction (CI) method. The differences in the Q-band absorptions among the isomers are clearly explained by the four-orbital model.

Quasi-relativistic ab initio calculations are performed for (super 199)Hg nuclear magnetic shielding constants and chemical shifts in a series, which included spin free relativistic (SFR) term and magnetic interaction (RMI) term. It is important to increase in the flexibility of the innermost and outermost orbitals of the basis set.

A study was conducted to calculate the excitation energies and oscillator strengths for the singlet excited states of the two molecules with high electron affinity, namely, the octahedral molybdenum hexafluoride (MoF6) and the molecule MoOF4 derived from the oxidation of MoF6 using MoO3. The results of these electronic-structure investigations using symmetry adapted cluster(SAC) and SAC-configuration interaction methods are discussed.