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Second harmonic generation (SHG) is a nonlinear optical phenomenon where two photons at the frequency ω combine to form a single photon at the second-harmonic frequency 2ω. Since that second-order process is very weak in bulk isotropic media, optical SHG responses of interfaces provide a powerful and versatile technique to probe the molecular structure and dynamics of liquid interfaces. Both local dipole contributions and non-local quadrupole contributions can be interesting to investigate different properties of the interface, such as the molecular orientation or the charge density. However, a major difficulty is to comprehend the link between the S-SHG intensity and molecular details. This article reports a numerical approach to model the polarization-resolved SHG intensities of a model vapor/liquid interface of pure water. The influence of the interfacial local environment on the hyperpolarizability is taken into account using quantum mechanical/molecular mechanics calculations. The numerical predictions are in very good agreement with experiments. We detail the hypotheses made during the modeling steps and discuss the impact of various factors on the modeled SHG intensities, including the description of the exciting field in the interfacial layer, the effect of neighboring molecules on the second-harmonic polarization, and the presence of an additional static electric field at the interface. [ABSTRACT FROM AUTHOR]

The optical second harmonic (SH) response from gold metallic nanocylinders with diameters of 80 and 120 nm arranged in hexagonal arrays has been determined as a function of the input fundamental polarization angle for the on- and off-axis transmission geometries and crossed output polarization configurations. For the on-axis transmission geometry, the nonlinear response of the nanocylinders is shown to be mainly incoherent, of pure electric dipole nature and arising from the breaking of the centrosymmetric shape of the body of the cylinders in a plane parallel to the substrate surface. Small angle off-axis experiments however show that the coherent contribution to the nonlinear response is size dependent suggesting that, besides the out-of-plane nonlinearity, retardation effects may also play a nonnegligible role. [ABSTRACT FROM AUTHOR]

Hyper Raleigh scattering, a common technique to investigate the second harmonic light scattered from a liquid suspension of molecular compounds and to determine their quadratic hyperpolarizability, has been used for aqueous suspensions of gold nanoparticles, the diameter of which ranges from 20 up to 150 nm. The hyper Rayleigh signal intensity was recorded as a function of the angle of polarization of the incident fundamental wave. For the particles with a diameter smaller than 50 nm, the response is dominated by the dipolar contribution arising from the deviation of the particle shape from that of a perfect sphere. For larger diameter particles, retardation effects in the interaction of the electromagnetic fields with the particles cannot be neglected any longer and the response deviates from the pure dipolar response, exhibiting a strong quadrupolar contribution. It is then shown that in order to quantify the relative magnitude of these two dipolar and quadrupolar contributions, a weighting parameter ζV which equals unity for a pure quadrupolar contribution and vanishes for a pure dipolar response, can be introduced. [ABSTRACT FROM AUTHOR]

Studies the metallicity of lithium rich Li[sub n]H[sub m, sup +] cluster ions by measuring unimolecular dissociation rates. Decomposition of the cluster ions by evaporation of a Li atom or a Li[sub 2] molecule; Metal cluster characteristics of the evaporative rates of mixed clusters.

The present paper gives the experimental results obtained in a centrifugal compressor stage designed and built by SAFRAN Helicopter Engines. The compressor is composed of inlet guide vanes, a backswept splittered unshrouded impeller, a splittered vaned radial diffuser and axial outlet guide vanes. Previous numerical simulations revealed a particular S-shape pressure rise characteristic at partial rotation speed and predicted an alternate flow pattern in the vaned radial diffuser at low mass flow rate. This alternate flow pattern involves two adjacent vane passages. One passage exhibits very low momentum and a low pressure recovery, whereas the adjacent passage has very high momentum in the passage inlet and diffuses efficiently. Experimental measurements confirm the S-shape of the pressure rise characteristic even if the stability limit experimentally occurs at higher mass flow than numerically predicted. At low mass flow the alternate stall pattern is confirmed thanks to the data obtained by high-frequency pressure sensors. As the compressor is throttled the path to instability has been registered and a first scenario of the surge inception is given. The compressor first experiences a steady alternate stall in the diffuser. As the mass flow decreases, the alternate stall amplifies and triggers the mild surge in the vaned diffuser. An unsteady behavior results from the interaction of the alternate stall and the mild surge. Finally, when the pressure gradient becomes too strong, the alternate stall blows away and the compressor enters into deep surge. [ABSTRACT FROM AUTHOR]

Full annulus simulations of the flow which develops in a transonic centrifugal compressor are performed at two stable operating points (peak efficiency and near surge) and during the path to surge. At stable conditions, the flow field properties are analyzed by comparisons with experimental data and numerical simulations using a phase lagged approach previously carried out. Regarding the stage overall performance, an excellent agreement is obtained between the numerical results (both with time lagged approach and full-annulus calculation) and the experiments. From the full-annulus simulations, the change in flow pattern from peak efficiency to surge is found to be perfectly similar to that obtained from the simulations using the time lagged approach. In particular, provided that the operating point is stable, the flow proves to be chorochronic. The full-annulus simulations were continued after a unique small change in the throttle law applied at the exit of the numerical domain. The mass flow, pressure ratio and efficiency then significantly drop all the more the time progresses. The simulation becomes unstable and the surge inception well underway. The path to surge is found to be due to the enlargement of the boundary layer separation on the suction side of the diffuser vanes in accordance with the conclusions drawn from the chorochronic simulations and experiments. But as the time progresses, the flow loses its chorochronic character. Stall cells rotating at around 7% of the rotor speed develop and lead to surge in around 5 revolutions. [ABSTRACT FROM AUTHOR]

The interface dynamic properties of a monoamide extractant with potential for application to the front end of the nuclear cycle and to waste treatment are examined by second harmonic generation. The results are compared with bulk nitric ion titration and surface pressure measurements. SH static studies show the extractant reaching the interface and accurately match the IFT measurements. The main feature of the SH dynamic studies is a chaotic fluctuation period, strongly related to intense extraction. Fluctuations are a signature of the interface behaviour during the extraction process. Vertical development of the interface, often called protrusion, remains the most probable origin of the measured fluctuation. Additionally, interfacial measurements show a non-monotonic lag time during extraction, probably related to cooperative effects not observed in the bulk at the working concentration. Such mutual behaviour could be a supplementary prerequisite for the ion transfer across this liquid–liquid interface. [ABSTRACT FROM AUTHOR]

We have measured the electric dipole moment of isolated alkali-C60 molecules (with alkali = Li, Na, K, Rb, and Cs) by molecular beam deflection experiments. The dipole increases from 12.4 D for LiC60 to 21.5 D for CsC60. These results are compared to those deduced from an analytical polarizable-ion model. This comparison shows that there is a strong electron transfer from the alkali atom to the C60 cage, which is almost complete for KC60 and RbC60. [ABSTRACT FROM AUTHOR]

A non perturbative approach is used to solve the problem of a rigid linear molecule with both a permanent dipole moment and a static dipole polarizability, in a static electric field. Eigenenergies are obtained and compared to perturbative low field and high field approximations. Analytical expressions for the orientation parameters and for the gradient of the energy are given. This non perturbative approach is applied to the simulation of beam deviation experiments in strong electric field. Results of simulations are given for inhomogeneous alkali dimers. For LiNa, the simulations are compared to experimental data. For LiK, deviation profiles have been simulated in order to prepare future experiments on this molecule. [ABSTRACT FROM AUTHOR]

We have measured the static dipole polarizability of lithium and sodium clusters ( n=1-22). Values measured for sodium are in agreement with previous experiments. While the polarizability per atom for sodium clusters decreases slowly as a function of the cluster size, a sharp decrease between sizes 1 and 4 is observed for lithium clusters. Experimental values are compared to Density Functional Theory (DFT/PW91) calculations. The size evolutions for sodium and lithium cluster polarizabilities are well reproduced by our calculations. The sharp decrease observed for small lithium clusters is discussed in terms of electronic density. [ABSTRACT FROM AUTHOR]

The unimolecular decomposition of metal rich LiH clusters (1 ≤ m ≤ 6, n ≤ 22 and ( n − m) > 3) is studied. The evaporative rates of the mixed clusters display features characteristic of metallic clusters. This confirms and extends to a larger size range the previous results obtained by photoionization and absorption cross section measurements. The evaporative rates are simulated by considering that there is a segregation between a metallic Li part and an insulating (LiH) part in the mixed cluster. [ABSTRACT FROM AUTHOR]

Analyzes the direct measurement of the electric polarizability of isolated carbon[sub 60] molecules by molecular beam deflection technique. Generation of the molecular beam with a laser vaporization source; Deflection measurements; Arrival time distribution profiles of molecules; Factors affecting precision on the value of polarizability.