Chloroform infrared multiphoton dissociation in the presence of O2 and NO2

The infrared multiphoton dissociation (IRMPD) of CDCl3 in the presence of O2 and NO2 as acceptor gases has been studied. We have worked with both pure CDCl3 and mixtures with CHCl3. The reaction mechanism following IRMPD of CDCl3 is discussed in detail. CCl2O, CCl4 and DCl were found to be the main products. With added O2, the observed CDCl3 dissociation was larger than with nonoxygenated acceptor gases. The reaction mechanism probably involves a catalytic cycle initiated by the oxidation of CCl3. With the aim of discriminating the different CDCl3 dissociation mechanisms, the IRMPD of CDCl3 in the presence of NO2 was first studied. In order to make evident the CDCl3 dissociation produced by the catalytic cycle, we then studied the IRMPD of CDCl3 in mixtures with CHCl3 with O2 as the acceptor gas. In this case, the dissociation mechanism subsequent to IRMPD is evidenced in the competence between the two isotopic species.     

Velocity fluctuations in laminar fluid flow

Fluctuating hydrodynamics, originally developed for fluctuations in fluids in equilibrium, can be extended to deal also with thermally excited hydrodynamic fluctuations in non-equilibrium states. After first reviewing some results earlier obtained for temperature fluctuations in fluids subjected to an externally imposed temperature gradient, we use in this paper fluctuating hydrodynamics to determine the enhancement of velocity fluctuations in laminar fluid flow. Adopting the case of planar Couette flow as a representative example, we show how the fluctuations of the wall-normal component of the velocity and of the wall-normal component of the vorticity can be obtained as solutions of a stochastic Orr–Sommerfeld equation and a stochastic Squire equation, respectively. By solving these fluctuating hydrodynamic equations we obtain quantitative estimates of the flow-induced non-equilibrium enhancements of the velocity and vorticity fluctuations as a function of the Reynolds number and of the wave number of the fluctuations.     

Silica-based powders and monoliths with bimodal pore systems

Porous pure and doped silicas with pore sizes at two length scales (meso/macroporous) have been prepared and shaped both as powders and monoliths through a one-pot surfactant assisted procedure by using a simple template agent and starting from atrane complexes as inorganic precursors.     

Low-frequency velocity correlation spectrum of fluid in a rectangular microcapillary

In addition to the fast correlation for local stochastic motion, the velocity correlation function in a fluid enclosed within the pore boundaries features a slow long time-tail decay. At late times, the flow approaches that of an incompressible fluid. Here, we consider the motion of a viscous fluid, at constant temperature, in a rectangular semipermeable channel. The fluid is driven through the rectangular capillary by a uniform main pressure gradient. Tiny pressure gradients are allowed perpendicular to the main flux. We solve numerically the three-dimensional Navier-Stokes equations for the velocity field to obtain the steady solution. We then set and solve the Langevin equation for the fluid velocity. We report hydrodynamic fluctuations for the center-line velocity together with the corresponding relaxation times as a function of the size of the observing region and the Reynolds number. The effective diffusion coefficient for the fluid in the microchannel is also estimated (Deff = 1.43 x 10(-10) m2.s-1 for Re = 2), which is in accordance with measurements reported for a similar system (Stepisnik, J.; Callaghan, P. T. Physica B 2000, 292, 296-301; Stepisnik, J.; Callaghan, P. T. Magn. Reson. Imaging 2001, 19, 469-472).     

Nanoparticulated silicas with bimodal porosity: chemical control of the pore sizes

Nanoparticulated bimodal porous silicas (NBSs) with pore systems structured at two length scales (meso- and large-meso-/macropores) have been prepared through a one-pot surfactant-assisted procedure by using a simple template agent and starting from silicon atrane complexes as hydrolytic inorganic precursors. The final bulk materials are constructed by an aggregation of pseudospherical mesoporous primary nanoparticles process, over the course of which the interparticle (textural) large pore system is generated. A fine-tuning of the procedural variables allows not only an adjustment of the processes of nucleation and growth of the primary nanoparticles but also a modulation of their subsequent aggregation. In this way, we achieve good control of the porosity of both the intra- and interparticle pore systems by managing independent variables. We analyze in particular the regulating role played by two physicochemical variables: the critical micelar concentration (cmc) of the surfactant and the dielectric constant of the reaction medium.     

Rate measurement of the reaction of CF2Cl radicals with O2

We have studied the association reaction of the CF(2)Cl radicals with O(2) in presence of N(2). The infrared multiple photon dissociation (IRMPD) technique with a homemade TEA CO(2) laser was used for the CF(2)Cl radical generation and the vibrational chemiluminiscence technique was set up for the study of the reaction kinetics. The time-resolved IR fluorescence of the vibrationally excited CF(2)O photoproduct was used to measure the disappearance rate of these radicals. A kinetic mechanism is presented to account for the rate of production of CF(2)O(*). The CF(2)Cl radical association reaction rate with O(2), evidence of a direct channel of photoproduct formation and its reaction rate, and the CF(2)O(*) collisional deactivation rate have been obtained.     

Alkaline earth fluoride and Eu3+ doped thin films obtained by electrochemical processing

Journal of Solid State Electrochemistry - In this study, alkaline earth fluorides (MF2) and MF2:Eu3+ doped (M = Mg, Ca, Sr) thin films were obtained by electrochemical processing. In...