Uniform and highly surface-enhanced Raman spectroscopic (SERS)-active substrates have been fabricated using Ag nanoparticle arrays with unprecedented small tunable gaps. The dependence of the enhancing capability of the substrate on the gap size provides quantitative evidence for the collective SERS effect and confirms predictions of interparticle-coupling-induced Raman enhancement.

The electronic and geometrical properties of distyrylbenzene (DSB) are investigated by using chemistry theoretical calculation methods. Specifically, the excited state properties are studied by performing ab initio correlation interaction singlet (CIS) and time-dependent density functional theory; the ground state and Raman activities are computed by density functional theory with the B3LYP method. Eight conformers of distyrylbenzene are found and they are derived from three isomers which are cis, cis-, cis, trans-, and trans, trans-, respectively. The relative energy shows that each isomer of three types is separated with a large energy barrier, but a small energy difference of each conformer is found if they are in the same type. The transition state also shows the barrier between conformers is lower than isomers. The computed excited transition energies using ZINDO/S based on the optimized geometries at a DFT/B3LYP level with 6–31+G show an excellent agreement with experimental absorption spectra.

A combined analytical–numerical study is presented for the quasisteady photophoretic motion of a spherical aerosol particle of arbitrary thermal conductivity and surface properties exposed to a radiative flux perpendicular to a large plane wall. The Knudsen number is assumed to be so small that the fluid flow is described by a continuum model with a temperature jump, a thermal slip, and a frictional slip at the surface of the radiation-absorbing particle. In the limit of small Peclet and Reynolds numbers, the appropriate equations of conservation of energy and momentum for the system are solved using a boundary collocation method and numerical results for the photophoretic velocity of the particle are obtained for various cases. The presence of the neighboring wall causes two basic effects on the particle velocity: first, the local temperature gradient on the particle surface is enhanced or reduced by the wall, thereby speeding up or slowing down the particle; second, the wall increases viscous retardation of the moving particle. The net effect of the wall can decrease or increase the particle velocity, depending upon the relative conductivity and surface properties of the particle as well as the relative particle–wall separation distance. In general, the boundary effect of a plane wall on the photophoresis of an aerosol particle can be quite significant in some situations. In most aerosol systems, the boundary effect on photophoresis is weaker than that on the motion driven by a gravitational field.

We report a study of excited-state dynamics of trans,trans-distyrylbenzene in hexane solution with femtosecond two-color transient absorption spectroscopy. Excited-state spectra at different pump–probe time delays were extracted and exhibit a spectral shift in 10ps. This 10-ps transient behavior is proposed to reflect an energy transfer process to a new intermediate state and the transferred population then relaxes through emitting photons. Its implications for photoisomerization and the comparison with trans-stilbene are discussed.

A low-temperature electrochemical synthesis of water-stabilized K(x)CoO(2)(.)yH(2)O crystal has been demonstrated. Temperature variable X-ray diffractions display a sandwiched structure with mobile water molecules. The crystal has hexagonal characteristic with four adjustable phases K(0.35)CoO(2)(.)0.40H(2)O, K(0.35)CoO(2)(.)0.34H(2)O, K(0.22)CoO(2)(.)0.21H(2)O, and anhydrous K0.15CoO2. Lattice water removal in a step-by-step process with the reduction of interlayer spacing in a single crystal can be achieved. Strong anisotropic conducting at low temperature and weak interlayer coupling in the ab plane have been demonstrated.

In this paper, using the dipole-dipole interactions to describe the interaction between the system molecule and medium molecules, a theory of medium-induced optical activity has been developed. We have shown that the symmetry technique can be used to determine the types of electronic states that can be involved in the medium-induced optical activity and that the octant rule can be deduced by using our theory.

b Cen ter for Con densed Mat ter Sci ence, Na tional Tai wan Uni ver sity, Tai pei, Tai wan, R.O.C. c Department of Chem is try, Na tional Tai wan Uni ver sity, Tai pei, Tai wan, R.O.C. In this pa per, us ing the di pole-dipole in ter ac tions to de scribe the in ter ac tion be tween the sys tem mol e cule and me dium mol e cules, a the ory of me dium-induced op ti cal ac tiv ity has been de vel oped. We have shown that the sym me try tech nique can be used to de ter mine the types of elec tronic states that can be in volved in the me - dium-induced op ti cal ac tiv ity and that the octant rule can be de duced by us ing our the ory.

Basic theoretical treatments of quantum beats are presented using the effective Hamiltonian method and the density matrix method. To describe the states involved in quantum beats, the molecular-eigen state basis set and the zeroth order basis set are introduced. Based on these basis sets for the two-state model, the condition under which molecular coherence can be created is discussed.