Pure surface plasmon resonance enhancement of the first hyperpolarizability of gold core-silver shell nanoparticles

We report the optical second harmonic (SH) response from gold core-silver shell nanoparticles supported at a liquid-liquid interface in the spectral region where the second harmonic generation (SHG) frequency is resonant with the surface plasmon (SP) resonance excitation of the nanoparticles. We compare these results with that obtained by classical linear optical absorption spectroscopy and show that the nonlinear optical response is dominated by the SP resonance enhancement with negligible contributions from the interband transitions. As a result, the SH spectrum exhibits two clear SP resonance bands attributed to the two SP resonances of the composite nanostructure formed by the gold core-silver shell nanoparticles. Absolute values of the hyperpolarizabilities are measured by hyper Rayleigh scattering (HRS) and compared that of pure gold nanoparticles. The hyperpolarizability measured at a harmonic energy of 3.0 eV, enhanced through excitation of the high energy SP resonance of the nanoparticle, increases with the silver content whereas the hyperpolarizability measured at a harmonic energy of 2.4 eV, enhanced through the excitation of the low energy SP resonance of the nanoparticle, decreases because of the shift of this resonance away from the harmonic frequency. The hyperpolarizability determined by HRS and the square root of the SHG intensities, scaling with the nanoparticle hyperpolarizability, have similar trends with respect to the silver content indicative of closely related adsorption properties yielding similar surface concentrations at the liquid-liquid interface.     

The explanation of high specificity of discriminating optical isomers in enzymatic reactions by the molecular anvil model of enzyme

The molecular anvil model of enzyme is proposed and applied to explain high specificity of discriminating optical isomers in enzymatic reactions. The molecular anvil is a mechanism which can accumulate energy from two interacting molecules and produce locally a high energy spot called anvil site. Two conditions neccessary for formation of the molecular anvil are described. For a pair of enzyme and substrate molecules these two conditions are considered to be satisfied. Assuming proper shapes and sizes for molecules of optical isomers and a hole on the surface of the enzyme molecule into which the optical isomers can fit and also assuming Lenard-Jones 12-6 type potential for each pair of interacting molecular sites. The amount of energy accumulated at the anvil site is calculated. Following the assumption that the total reactivity is determined by binding process and chemical process in which the accumulated energy at the anvil site is utilized to enhance the reaction, total reactivities for L- and D-isomers are calculated and the values of specificity of discriminating L-isomer from D-isomer are derived for various values of interaction energy. It is shown that the molecular anvil plays an important role in elevating specificity as well as producing high catalytic power of enzyme.     

Intersections of potential energy surfaces of short-lived states: the complex analogue of conical intersections

Whereas conical intersections between potential energy surfaces of bound states are well known, the interaction of short-lived states has been investigated only rarely. Here, we present several systematically constructed model Hamiltonians to study the topology of intersecting complex potential energy surfaces describing short-lived states: We find the general phenomenon of doubly intersecting complex energy surfaces, i.e., there are two points instead of one as in the case of bound states where the potential energy surfaces coalesce. In addition, seams of intersections of the respective real and imaginary parts of the potential energy surfaces emanate from these two points. Using the Sigma* and Pi* resonance states of the chloroethene anion as a practical example, we demonstrate that our complete linear model Hamiltonian is able to reproduce all phenomena found in explicitly calculated ab initio complex potential energy surfaces.     

On the relation between quantum lifetimes and classical stability for the systems with a saddle-type potential

Relations between quantum-mechanical and classical properties of open systems with a saddle-type potential, for which at a given energy only one unstable periodic orbit exists, are studied. By considering the convergence of the Gutzwiller trace formula [J. Math. Phys. 12, 343 (1971)] it is confirmed that both for homogeneous and inhomogeneous potentials the poles of the formula are located below the real energy axis, i.e., these kind of potentials do not support bound states, in general. Within the harmonic approximation the widths of resonant (transition) states are proportional to the values of Lyapunov exponent of the single periodic orbit calculated at the energies which are equal to the resonance positions. The accuracy of the semiclassical relation is discussed and demonstrated for several examples.     

Comparisons of measured rate constants with spectroscopically determined electron-transfer parameters

This work involves comparison of rate constants measured for an intervalence (IV) compound with electron-transfer parameters derived from its optical absorption spectrum. The temperature-dependent rate constants for the radical cation having 3-tert-butyl-2,3-diazabicyclo[2.2.2]oct-2-yl (hydrazine) charge-bearing units attached para to a tetramethylbenzene bridge (1+) were previously measured. In this study, resonance Raman is used to calculate the magnitudes of the distortions of normal modes of vibration caused by excitation into the intervalence absorption band. These data produce a vibrational reorganization energy lambdavsym of 9250 cm(-1), and averaged single-mode omegav for use in the Golden Rule equation of 697 cm(-1). Zhu-Nakamura theory has been used to calculate preexponential factors for analysis of the previously measured variable temperature optical spectra using quartic-enhanced intervalence bands to extract the total reorganization energy and the intramolecular electron-transfer rate constants for intramolecular electron transfer using electron spin resonance. In contrast to using the Golden Rule equation, separation of lambda into solvent and vibrational components is not significant for these data. The Zhu-Nakamura theory calculations produce ln(k/T) versus 1/T slopes that are consistent with the experimental data for electronic couplings that are somewhat larger than the values obtained from the optical spectra using Hush's method.     

Tunneling molecular dynamics in the light of the corpuscular-wave dualism theory

This paper presents the experimental demonstration of the corpuscular-wave dualism theory. The correlation between the de Broglie wavelength related to the thermal motion and the potential barrier width and height is reported. The stochastic jumps of light atoms (hydrogen, deuterium) between two equilibrium sites A and B (identical geometry) occur via different pathways; one pathway is over the barrier (classical dynamics), and the other one is through the barrier (tunneling). On the over-the-barrier pathway, there are no obstacles for the de Broglie waves, and this pathway exists from high to low temperatures up to 0 K because the thermal energy is subjected to the Maxwell distribution and a certain number of particles owns enough energy for the hopping over the barrier. On the tunneling pathway, the particles pass through the barrier, or they are reflected from the barrier. Only particles with the energy lower than barrier heights are able to perform a tunneling hopping. The de Broglie waves related to these energies are longer than the barrier width. The Schr?dinger equation is applied to calculate the rate constant of tunneling dynamics. The Maxwell distribution of the thermal energy has been taken into account to calculate the tunneling rate constant. The equations for the total spectral density of complex motion derived earlier by us together with the expression for the tunneling rate constant, derived in the present paper, are used in analysis of the temperature dependence of deuteron spin-lattice relaxation of the ammonium ion in the deuterated analogue of ammonium hexachloroplumbate ((ND4)2PbCl6). It has been established that the equation CpTtun = EH (thermal energy equals activation energy), where Cp is the molar heat capacity (temperature-dependent, known from literature), determines directly the low temperature Ttun at which the de Broglie wavelength, lambdadeBroglie, related to the thermal energy, CpT, is equal to the potential barrier width, L. Above Ttun, the lambdadeBroglie wavelength related to the CpT energy is shorter than the potential barrier width and not able to overcome the barrier. The activation energy EH equals 7.5 kJ/mol, and therefore, the Ttun temperature for deuterons in ((ND4)2PbCl6 is 55.7 K. The agreement between the potential barrier width following from the simple geometrical calculations (L = 0.722 A) and de Broglie wavelength at Ttun (L = 0.752 A) is good. The temperature plots of the deuteron correlation times for (ND4)2PbCl6 reveal comparable values of the correlation times of the tunneling, (tau(T)), and over-the-barrier jumps (tau(H)) near 34.8 K. Matsuo, on the basis of the molar heat capacity study, found the first-order phase transition at this temperature.     

Quantum stochastic resonance in parity violating chiral molecules

In order to explore parity violating effects in chiral molecules, of interest in some models of evolution towards homochirality, quantum stochastic resonance (QSR) is studied for the population difference between the two enantiomers of a chiral molecule (hence for the optical activity of the sample), under low viscous friction and in the deep quantum regime. The molecule is described by a two-state model in an asymmetric double well potential where the asymmetry is given by the known predicted parity violating energy difference (PVED) between enantiomers. In the linear response to an external driving field that lowers and rises alternatively each one of the minima of the well, a signal of QSR is predicted only in the case that the PVED is different from zero, the resonance condition being independent on tunneling between the two enantiomers. It is shown that, at resonance, the fluctuations of the first order contribution to the internal energy are zero. Due to the small value of the PVED, the resonance would occur in the ultracold regime. Some proposals concerning the external driving field are suggested.     

Biased Brownian motion as the operating principle for microscopic engines

The hydrolysis of adenosine triphosphate (ATP) has been shown to drive the motion of motor proteins along a biopolymer. These motor proteins are the smallest engines known and, in the absence of an ATP-to-adenosine diphosphate chemical potential, they execute Brownian motion. Therefore, it is reasonable to imagine that the energy released in ATP hydrolysis is used to bias, or rectify, Brownian motion in one direction. In this paper, we show, in terms of Fokker-Planck equations that we solve analytically, how a net flow can occur along a periodic potential, provided that this potential has an anisotropy and that there is an energy input. We work out two cases: one case where the energy input comes from a fluctuation of the periodic potential in time and one case where a variation of temperature within a period is maintained. An interesting feature of these systems is that they need “the correct amount” of thermal noise. Without thermal noise or with too much thermal noise, no net flow occurs and, in this sense, the systems we discuss are one more example of the lately much discussed phenomenon of stochastic resonance.     

On the planarity and resonance effect of tetraphenylporphyren and its metallocomplexes

Based on Lennard-Jones potential and resonance effect calculations it has been demonstrated that in solution tetraphenylporphyrin assumes a structure closer to coplanar by 17° from that in the solid state. In the case of metalloporphyrin the tendency towards coplanarity is even greater, about 40°. The minimum in the energy curve is of the same order of magnitude as reported values of free energy of activation for the phenyl rotation.     

Cu nanoshells: effects of interband transitions on the nanoparticle plasmon resonance

The optical properties of metals arise both from optical excitation of interband transitions and their collective electronic, or plasmon, response. Here, we examine the optical properties of Cu, whose strong interband transitions dominate its optical response in the visible region of the spectrum, in a nanoshell geometry. This nanostructure permits the geometrical tuning of the nanoparticle plasmon energy relative to the onset of interband transitions in the metal. Spectral overlap of the interband transitions of Cu with the nanoshell plasmon resonance results in a striking double-peaked plasmon resonance, a unique phenomenon previously unobserved in other noble or coinage metal nanostructures.     

Studying the interaction between silica nanoparticles and metals by spectrophotometry

The optical absorption spectra of water silica sols containing nanoparticles (NPs) of metals (Ag, Pd, Fe, and Pt) are investigated. Silica sols are obtained from natural hydrothermal solutions via membrane concentration (ultrafiltration). Water sols of silica with specific sizes, pH values, ζ potentials of SiO₂ NP surfaces, and low concentrations of SiO₂ NPs are used. Plasmon resonance in optical absorption spectra is used to study the interaction between silica and metal NPs. Parameters of plasmon resonance (position, height, and half-width of optical absorption bands), from which the degree of interaction is assessed, are determined. Relationships between the optical properties of the surfaces of nanoparticle-size silica particles, the method of their production, and the effect of adsorbed metal particles on these properties are established.     

Investigations of the optical spectra and EPR parameters in CaWO4:Yb3+

In this paper, we calculate the optical spectra data (crystal-field energy levels), the electron paramagnetic resonance (EPR) g factors gparallel, gperpendicular of Yb3+ and hyperfine structure constants Aparallel, Aperpendicular of 171Yb3+ and 173Yb3+ isotopes in CaWO4 crystal in a unified way from the crystal-field theory. All the calculated results are in good agreement with the experimental values. The signs of Aparallel and Aperpendicular for both isotopes 171Yb3+ and 173Yb3+ are suggested.     

Enhancement of second harmonic generation in helical Sc liquid crystals

In a ferroelectric liquid crystal, a special type of phase-matching for optical second harmonic generation (SHG) is possible, where two counter-propagating fundamental waves create second harmonic waves at the edge of the selective reflection band. We compute the SHG intensity in such a situation and show that, at slight detuning from exact phase-matching, useful resonance enhancement can be obtained. A considerable amount of SHG also appears when the second harmonic frequency is in the reflection band, where the SHG wave is non-propagating.     

Measurements of accelerator beam spectrum through dependence of Cherenkov radiation intensity on phase velocity of electromagnetic waves in optical and microwave ranges

The use of Cherenkov radiation in the optical and microwave ranges for measuring the accelerator beam energy and the energy spectrum is described. Suggested methods are based on a dependence of the radiation intensity on the phase velocity of electromagnetic waves in the Cherenkov radiator medium. Mathematical procedure of extraction of the energy spectrum from the measured intensity is given in detail.     

表面等离子体波共振与常规检测技术的联用

表面等离子体波共振(SPR)是被入射电磁波所激发、存在于金属和电介质界面上电荷密度振动的谐振波.SPR是一种消逝场光学成功应用的典范,它具有体积小、分辨率高、无需标记、抗电磁干扰能力强等特点.本文介绍了SPR与电化学方法(循环伏安法、溶出伏安法)、光学方法(荧光光谱、红外光谱)、质谱和石英晶体微天平等其它常规检测技术联用的研究进展,与其它常规方法联用能进一步提高分析能力,可弥补彼此的不足.本文还特别详细说明了部分电化学方法、干涉测量法与表面等离子体波共振联用的优势及不足.     

Recoil frame photoelectron angular distributions of BF3: a sensitive probe of the shape resonance in the F 1s continuum

Recoil frame photoelectron angular distributions (RFPADs) of BF(3) molecules are presented over the energy region of the shape resonance in the F 1s continuum. Time-dependent density functional theory calculations are also given to understand the shape resonance dynamics. The RFPADs have been compared with the theoretical calculations. It is found that the RFPADs calculated by the localized core-hole model are in better agreement with the experimental, compared with those by the delocalized core hole. Dipole matrix elements and dipole prepared continuum wavefunctions show that the shape resonance in the F 1s ionization continuum of BF(3) is induced by p-partial waves as previously reported by Swanson et al. [J. Chem. Phys. 75, 619 (1981)]. However, due to the couplings with the other partial waves the feature characteristic of the p-partial waves has not been observed in the RFPADs.     

Electronic, linear, and nonlinear optical properties of III-V indium compound semiconductors

We have made an extensive theoretical study of the electronic, linear, and nonlinear optical properties of the III-V indium compound semiconductors InX (X=P, As, and Sb) with the use of full potential linear augmented plane wave method. The results for the band structure, density of states, and the frequency-dependent linear and nonlinear optical responses are presented here and compared with available experimental data. Good agreement is found. Our calculations show that these compounds have similar electronic structures. The valence band maximum and the conduction band minimum are located at Gamma resulting in a direct energy gap. The energy band gap of these compounds decreases when P is replaced by As and As by Sb. This can be attributed to the increase in bandwidth of the conduction bands. The linear and nonlinear optical spectra are analyzed and the origin of some of the peaks in the spectra is discussed in terms of the calculated electronic structure. The calculated linear optical properties show very good agreement with the available experimental data. We find that the intra-and interband contributions of the second-harmonic generation increase when moving from P to As to Sb. The smaller energy band gap compounds have larger values of chi(123) ((2))(0) in agreement with the experimental measurements and other theoretical calculations.     

Optical properties of the poly(N-benzylaniline) thin film

The optical properties of the poly(N-benzylaniline) thin film were investigated by optical characterization. The optical constants such as refractive index and dielectric constant were determined from the transmittance and reflectance spectra of the film. The refractive index dispersion was analyzed by the Wemple-DiDomenico model. The n(infinity) values changed from 6.37 to 5.71 and these values did not show any certain trend with annealing temperatures. The average oscillator parameter So value, which is the strength of the individual dipole oscillator, was found to be in the range of 1.15 x 10(13) to 1.03 x 10(13) m(-2). The optical band was determined from the direct optical transitions in K space. The optical band Eg of the film decreases from 2.089 to 2.046 eV with increasing annealing temperatures while the Urbach energy Eu called the width of localized states in the optical band gap increases from 0.544 to 0.598 eV. Consequently, the optical constants and optical band gap of the poly(N-benzylaniline) change with the annealing temperatures.     

Iodine-starch clathrate complexes under the impact of a low-frequency acoustic field

The results from research on the kinetics of destruction of clathrate complexes (amyloidine, amylopectoiodine and iodinol) in low-frequency acoustic waves from 5 to 25 Hz are presented. Features of the transfer of energy from low-frequency acoustic oscillations are determined. The ability of systems containing biologically active clathrate structures to interact in resonance with external acoustic stimuli according to the energy state of the active part of iodine-containing compexes is confirmed. In the first approximation, such compounds can be regarded as model biochemical systems.     

Resonance frequencies of meniscus waves as a physical mechanism for a DNA biosensor

This paper presents a liquid surface biosensor whose potential applications are analogue to the well-known quartz crystal microbalance. The technique involved is based on the resonance of meniscus capillary waves here excited at a functionalized air-water interface. The strategy proposed in this paper can be seen as a promising way to avoid as much as possible any transfer of Blodgett type. Meniscus capillary waves supplied by the electrodynamical vibration of a brimful cylinder filled with water are used as a way to characterize the surface aging of an air-water interface covered by a lipidic monolayer. An optical technique based on one-dimensional interferometry is developed to measure continuously the resonant behavior of the surface elevation at the center of the cell around the natural frequencies of the meniscus waves. The frequency dependence of the wave amplitude is investigated during the transient regime associated to the immobilization of DNA strands at the lipidic matrix. Resonant frequencies are found to be very sensitive to the chemical loading supported by the air-water interface. The technique is seen as a mean to discriminate between single- and double-stranded DNA.