Two new xanthones from Hypericum japonicum

Two new xanthones, 1,6-dihydroxyisojacereubin-5-O-beta-D-glucoside (1) and 3,6,7-tri-hydroxy-1-methoxy-xanthone (2), were isolated from Hypericum japonicum. The structural elucidation of the isolated compounds were primarily based on HREIMS, EIMS, UV, IR, 1D-, and 2D-NMR analyses, including COSY, HMQC, HMBC, and NOESY correlations.     

Anisotropic effects in the optical spectra of magic metal clusters: the role of ionic structure

The effect of the ionic positions on the optical spectra of magic metal clusters is studied via pseudopotential perturbation theory. Electronic many-body effects are considered within perturbed time-dependent local-density-approximation. Quantitative agreement with recent experiments by Reiners et al. is obtained. In this way a natural explanation is obtained for the temperature dependence of the optical absorption of magic metal clusters.     

Modeling of configurations and third-order nonlinear optical properties of methyl silsesquioxanes

Configuration optimizations, excited state properties, and the frequency-dependent third-order nonlinear optical polarizabilities have been investigated on a series of methyl-silsesquioxane (MeT) cages [CH(3)SiO(1.5)](n) (n=4, 6, 8, and 10) using ab initio quantum mechanical methods coupled with the sum-over-states methods. The obtained electronic absorption spectra show a redshift as the cage size increases, and the absorption spectra are assigned as charge transfers from oxygen p type to silicon s type atomic orbitals. The calculated average third-order polarizabilities of in the three optical physical processes (third-harmonic generation, the electric-field-induced second-harmonic generation, and degenerate four-wave mixing) have wide nonresonance regions. For all the considered species, the values of gamma decrease in the order of [MeT](4)>[MeT](8)(C(2v))=[MeT](10)>[MeT](6)>[MeT](8)(O(h)).     

Study of 3d – 4f and 3d – 5f quartet and doublet transitions of doubly excited three-electron ions

We present the first observation of optical transitions between doubly excited doublet states in the term systems N V, O VI and F VII. The spectra were produced by foil excitation of fast ion beams. The assignment of the spectral lines was made by comparison with the results of MCDF calculations along the isoelectronic sequence. The same method also led to the identification of two 3d – 4f quartet transitions in Mg X.     

A theoretical investigation of hyperpolarizability for small Ga(n)As(m) (n + m = 4-10) clusters

In this paper, the second and third order polarizabilities of small Ga(n)As(m) (n + m=4-10) clusters are systematically investigated using the time dependent density functional theory (TDDFT)6-311+G* combined with the sum-over-states method (SOSTDDFT6-311+G*). For the static second order polarizabilities, the two-level term (beta(vec.2)) makes a significant contribution to the beta(vec) for all considered Ga(n)As(m) clusters except for the Ga3As4 cluster. And, for the static third order polarizabilities, the positive channel (gamma(II)) makes a larger contribution to gamma(tot) than the negative channel (gamma(I)). Similar to the cubic GaAs bulk materials, the small Ga(n)As(m) cluster assembled materials exhibit large second order (1 x 10(-6) esu) and third order susceptibilities (5 x 10(-11) esu). The dynamic behavior of beta(-2omega; omega, omega) and gamma(-3omega; omega, omega, omega) show that the small Ga(n)As(m) cluster will be a good candidate of nonlinear optical materials due to the avoidance of linear resonance photoabsorption.     

Observations of plasmons in warm dense matter

We present the first collective x-ray scattering measurements of plasmons in solid-density plasmas. The forward scattering spectra of a laser-produced narrow-band x-ray line from isochorically heated beryllium show that the plasmon frequency is a sensitive measure of the electron density. Dynamic structure calculations that include collisions and detailed balance match the measured plasmon spectrum indicating that this technique will enable new applications to determine the equation of state and compressibility of dense matter.     

Theoretical study on the photophysical properties of hexapyrrolidine C60 adducts with Th, D3, and S6 symmetries

The equilibrium geometries of three isomeric hexapyrrolidine C(60) adducts with T(h), D(3), and S(6) symmetries are optimized by means of the B3LYP method at the 6-31G basis sets in this paper. On the basis of the optimized structures, the excited state and third-order nonlinear optical properties, such as third-harmonic generation (THG), electric-field-induced second-harmonic generation (EFISHG), and degenerate four-wave mixing (DFWM), and two-photon absorption (TPA) cross sections, delta, are calculated by using the TDB3LYP model based on the 6-31G level coupled with the sum-over-states (SOS) method. The computational results show that the transition energies from S(0) to S(1) of the T(h) hexaadduct and the D(3) hexaadduct have a remarkable blue shift by comparison with that of the C(60) parent. These results are in agreement with experimental ones. However, the first singlet excitation energy of the S(6) hexaadduct has a red shift compared with that of the C(60) parent. Accordingly, we predict that different positions located by six addends may result in the different spectrum properties. Finally, the two-photon absorption cross sections indicate that the largest average value of resonant TPA, delta, of the D(3) hexaadduct has a red shift compared with those of the T(h) and S(6) hexaadducts.     

Self-diffusion study of poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) block copolymers in aqueous solution

The self-diffusion of poly (ethylene oxide)-poly (propylene oxide)-poly (ethylene oxide) block copolymers dissolved in deuterated water was investigated by means of pulsed field gradient NMR (PFG-NMR). The polymer forms micelles in the solution and, with increasing temperature, clouding and phase demixing occurs. The self-diffusion coefficient indicates the association of the polymer molecules in the vicinity of the cloud point because of its maximum with increasing temperature. Above the cloud point, two kinds of diffusing species are observed due to phase separation. The faster diffusing species is attributed to the polymer-poor phase. The self-diffusion coefficient of the polymer-rich phase species decreases with increasing temperature above the cloud point due to further association and dehydration. The correlation length of the diffusing associates, calculated from the self-diffusion coefficient and the viscosity by means of the Stokes-Einstein equation is nearly independent of temperature and concentration up to 30 wt-% polymer concentration. The correlation length is about 1.4 nm. It shows a slight maximum at the cloud point.     

Catalytic oxidation of ammonia on RuO2(110) surfaces: mechanism and selectivity

The selective oxidation of ammonia to either N2 or NO on RuO2(110) single-crystal surfaces was investigated by a combination of vibrational spectroscopy (HREELS), thermal desorption spectroscopy (TDS) and steady-state rate measurements under continuous flow conditions. The stoichiometric RuO2(110) surface exposes coordinatively unsaturated (cus) Ru atoms onto which adsorption of NH3 (NH3-cus) or dissociative adsorption of oxygen (O-cus) may occur. In the absence of O-cus, ammonia desorbs completely thermally without any reaction. However, interaction between NH3-cus and O-cus starts already at 90 K by hydrogen abstraction and hydrogenation to OH-cus, leading eventually to N-cus and H2O. The N-cus species recombine either with each other to N2 or with neighboring O-cus leading to strongly held NO-cus which desorbs around 500 K. The latter reaction is favored by higher concentrations of O-cus. Under steady-state flow condition with constant NH3 partial pressure and varying O2 pressure, the rate for N2 formation takes off first, passes through a maximum and then decreases again, whereas that for NO production exhibits an S-shape and rises continuously. In this way at 530 K almost 100% selectivity for NO formation (with fairly high reaction probability for NH3) is reached.