The photoinduced structural change of a prototype metal complex, [Cu(dmphen)(2)](+) (dmphen = 2,9-dimethyl-1,10-phenanthroline), was studied by ultrafast spectroscopy with time resolution as high as 30 fs. Time-resolved absorption measured with direct S(1) excitation clearly showed spectral changes attributable to the D(2d) (perpendicular) → D(2) (flattened) structural change occurring in the metal-to-ligand charge transfer singlet excited state ((1)MLCT) and the subsequent S(1) → T(1) intersystem crossing. It was confirmed that the two processes occur with time constants of ~0.8 ps (structural change) and ~10 ps (intersystem crossing), and their time scales are clearly well-separated. A distinct oscillation of the transient absorption signal was observed in the femtosecond region, which arises from the coherent nuclear motion of the perpendicular S(1) state that was directly generated by photoexcitation. This demonstrated that the perpendicular S(1) state has a well-defined vibrational structure and can vibrate within its subpicosecond lifetime. In other words, the S(1) state stays undistorted in a short period, and the coherent nuclear motion is maintained in this state. Time-dependent density functional theory (TDDFT) calculations gave consistent results, indicating a very flat feature and even a local minimum at the perpendicular structure on the S(1) potential energy surface. The vibrational assignments of the S(1) nuclear wavepacket motion were made on the basis of the TDDFT calculation. It was concluded that photoexcitation induces a(1) vibrations containing the Cu-ligand bond length change and a b(1) vibration attributed to the ligand-twisting motion that has the same symmetry as the flattening distortion. Ultrafast spectroscopy and complementary quantum chemical calculation provided an overall picture and new understanding of the photoinduced structural change of the prototypical metal complex.

With ab initio molecular orbital calculations, the structures of the cation clusters Mg+(H20)" and their hydrogen-eliminated products (Mg0H)+(H20)"-i are optimized. In Mg+(H20)", the hydration number of the most stable isomer is 3. In (Mg0H)+(H20)"-i, all water molecules are directly bonded to Mg+ for n < 6. The hydration energy of (MgOH)+ is larger than that of Mg+ because of the strongly polarized (MgOH)+ molecular ion; Mg is oxidized halfway to Mg(II). The internal energy change of the hydrogen elimination of Mg+(H20)" is positive for n = 1-5, but becomes negative for n = 6, which is in good agreement with the product switching in the TOF spectrum reported in the preceding paper by Sanekata et al. The effects of isotope substitution and equilibrium constants of the hydrogen (deuterium) elimination reaction observed in their experiment can be explained qualitatively.

We investigated the influence of surface hydroxyl groups (-OHs) on the supported planar phospholipid bilayer (SPB) formation and characteristics. We prepared SiO2 surfaces with different hydrophilicity degree by annealing the SiO2 layer on Si(100) formed by wet chemical treatments. The hydrophilicity reduced with irreversible thermal desorption of -OHs. We formed SPB of dimyristoylphosphatidylcholine on the SiO2 surfaces by incubation at a 100-nm-filtered vesicle suspension. The formation rate was faster on less hydrophilic surfaces. We proposed that a stable hydrogen-bonded water layer on the SiO2 surface worked as a barrier to prevent vesicle adhesion on the surface. Theoretical calculation indicates that water molecules on vicinal surface -OHs take a stable surface-unique geometry, which disappears on an isolated -OH. The surface -OH density, however, affected little the fluidity of once formed SPBs, which was measured by the fluorescence recovery after the photobleaching method. We also describe the area-selective SPB deposition using surface patterning by the focused ion beam.

Structure and vibrations of catechol and catecholH2O(D2O) in the S 0 and S 1 stateHigh resolution UV spectroscopy of phenol and the hydrogen bonded phenolwater cluster J. Chem. Phys. 104, 972 (1996); 10.1063/1.470821 Ab initio study of the structure of radical cations derived from Hbonded complexes: a comparison between [H2CO.H2O]+. and [H2CO.HF]+.The structures of the phenol-͑H 2 O͒ n clusters ͑nр4͒ are determined with ab initio molecular orbital methods, and their infrared spectra are calculated to analyze the experimental spectra reported in the preceding paper. The experimental infrared spectra of phenol-͑H 2 O͒ n clusters for nр4 have ''window regions,'' which are intervals of two types of OH stretching modes of the water molecules. The calculated IR spectra of isomers with a ring structure will reproduce these window regions. The ring is formed by a network of the hydration bonds of the ϪOH group of the phenol and water molecules. For nϭ4, two kinds of spectra are reported in the experiments. One spectrum has a window region similar to that of nр3. It is, therefore, identified to the isomers of a ring structure. The other one has several bands in the window region. The calculations for several isomers and large clusters suggest that this spectra might be attributed either ͑i͒ to the mixture of several branched isomers, ͑ii͒ to the products of evaporation of large clusters, or ͑iii͒ to the product of the proton transfer reaction in phenol-͑H 2 O͒ 4 cluster.

The geometric structures of 7-azaindole−water complexes, (7-AzI)-(H2O) n (n = 1−3), and 7-AzI dimer were investigated by laser-induced fluorescence (LIF) spectroscopy with high resolution (∼0.01 cm-1). For the 7-AzI−(H2O) n complexes (n = 1−3), the LIF spectra show partially resolved rotational structure, which has been analyzed in combination with theoretical calculations. This analysis yields the rotational constants and characterizes the structures. In 7-AzI−(H2O)1, the H2O molecule is located in the molecular plane, forming a six-membered ring with two hydrogen bonds. Analyses for 7-AzI−(H2O)2 and −(H2O)3 show, furthermore, that both the second and the third H2O are located in the molecular plane of 7-AzI, forming a network ring of hydrogen bonds. For the 7-AzI dimer, the LIF spectrum shows an unresolved rotational envelope. The rotational contour has been analyzed, and we discuss the dimer's likely structure.

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With ab initio molecular orbital calculations, structures of the singly positive charged boron−water clusters B+(H2O) n and aluminum−water clusters Al+(H2O) n are determined. The insertion reaction products HBOH+(H2O) n -1 and HAlOH+(H2O) n -1 are also investigated. Structures of the dimer-core clusters [M+(H2O)2](H2O) n -2 are similar to each other for M = B and Al. In contrast, the stability and structures of [B+(H2O)](H2O) n -1 and [Al+(H2O)](H2O) n -1 are quite different. The monomer-core boron clusters [B+(H2O)](H2O) n -1 do not have stable local minima; the spontaneous proton transfer reaction takes place to form BOH(H3O)+(H2O) n -2. In other words, the acid−base reaction takes place in such small clusters. In the larger clusters, the reaction further proceeds and the clusters isomerize to the linear type HBOH+(H2O) n -1. On the other hand, in the clusters [Al+(H2O)](H2O) n -1, no such reaction takes place. The cis-form hydrated products of the insertion reaction HMOH+(H2O) n -1 are more reactive, and the acid−base reaction is seen for both M = B and Al.

The reduced partition function ratio for lithium ions in an aqueous solution is derived from the extrapolation of the values of the reduced partition function ratio (r values can be calculated from the normal vibration frequencies according to Bigeleisen and Mayer's theory. To obtain the values of f n r , the normal vibration frequency calculations were carried out for optimized structures of [Li(H 2 O) n ] + (n ) 1-6) using the RHF/6-31+G(d), RHF/6-31++G(d,p), RHF/6-311+G(d) and MP2/6-31+G(d) methods by means of the ab initio molecular orbital method. All of those structures having high symmetry were confirmed to have real harmonic frequencies at the RHF/6-31+G(d) and RHF/6-31++G(d,p) levels. For the two RHF methods, the value of f n r increases to about 1.07 with an increase of the hydration number n, and reaches maximum at n ) 4. In the most stable isomers of [Li(H 2 O) n ] + clusters for n ) 5 and 6, respectively, the first hydration shell is saturated with the four water molecules, and the size dependence of the f n r values converges for n g 4. The converged value 1.07 can, therefore, be regarded as the reduced partition function ratio for lithium ions in aqueous solution, and gives the upper limit of the isotopic separation factor in an aqueous solution-exchanger system.