[1] During the Lindenberg Aerosol Characterization Experiment (LACE 98) simultaneous measurements with ground-based and airborne lidars and with two aircraft equipped with aerosol in situ instrumentation were performed. From the lidar measurements, particle backscatter coefficients at up to eight wavelengths between 320 and 1064 nm and particle extinction coefficients at 2-3 wavelengths between 292 and 532 nm were determined. Thus, for the first time, an extensive set of optical particle properties from several lidar platforms was available for the inversion into particle microphysical quantities. For this purpose, two different inversion algorithms were used, which provide particle effective radius, volume, surface-area, and number concentrations, and complex refractive index. The single-scattering albedo follows from Mie-scattering calculations. The parameters were compared to the ones from airborne measurements of particle size distributions and absorption coefficients. Two measurement cases were selected. During the night of 9 -10 August 1998 measurements were taken in a biomass-burning aerosol layer in the free troposphere, which was characterized by a particle optical depth of about 0.1 at 550 nm. Excellent agreement between remote-sensing and in situ measurements was found. In the center of this plume the effective radius was approximately 0.25 m, and all methods showed rather high complex refractive indices, ranging from 1.56 -1.66 in real part and from 0.05-0.07i in imaginary part. The single-scattering albedo showed low values from 0.78 -0.83 at 532 nm. The second case, taken on 11 August 1998, presents the typical conditions of a polluted boundary layer in central Europe. Optical depth was 0.35 at 550 nm, and particle effective radii were 0.1-0.2 m. In contrast to the first case, imaginary parts of the refractive index were below 0.03i. Accordingly, the single-scattering albedo ranged from 0.87-0.95.

The dynamics of molecular multiphoton ionization and fragmentation of a diatomic molecule (Na2) have been studied in molecular beam experiments. Femtosecond laser pulses from an amplified colliding-pulse moddocked (CPM) ring dye laser are employed to induce and probe the molecular transitions. The final continuum states are analyzed by photoelectron spectroscopy, by ion mass spectrometry and by measuring the kinetic energy of the formed ionic fragments. Pumpprobe spectra employing 70-fs laser pulses have been measured to study the time dependence of molecular multiphoton ionization and fragmentation. The oscillatory structure of the transient spectra showing the dynamics on the femtosecond time scale can best be understood in terms of the motion of wave packets in bound molecular potentials. The transient Na2+ ionization and the transient Na+ fragmentation spectra show that contributions from direct photoionization of a singly excited electronic state and from excitation and autoionization of a bound doubly excited molecular state determine the time evolution of molecular multiphoton ionization.

and optical modeling, we investigate the possible evolution of this cloud assuming either in situ freezing of ternary HNOa/H2SO4/H20 droplets as nitric acid trihydrate, or the formation of the clouds in mountain waves over the east coast of Greenland, as suggested by a mountain wave model. Best agreement with the observations was obtained by assuming mountain-wave-induced cloud formation, which yields nitric acid trihydrate particles with much higher total mass than achieved by assuming synoptic-scale freezing. Our analysis suggests that this rare type of PSC, which we term type Ia-enh, is characterized by nitric acid hydrate particles rather close to thermodynamic equilibrium, while the more common type Ia PSCs appear to contain much less mass than representative of equilibrium.

Based on reliable, carefully selected data sets, equations for the thermal conductivity and the viscosity of the refrigerant R 152a are presented. They are valid at temperatures from 240 to 440 K, pressures up to 20 MPa, and densities up to 1050 kg. rn -s, including the critical region.

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The surface tension γ of the room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate, [bmim][PF 6 ] in short, has been evaluated in the framework of Guggenheim's corresponding-states analysis using experimental data taken from the literature as well as new simulation data. The critical temperature is estimated to be T c ) 1100 K ( 100 K from the surface-tension data, which are analyzed in terms of the empirical expressions of Guggenheim and of Eo ¨tvo ¨s. Adopting this value of T c , a critical density of F c ) 0.35 g cm -3 ( 0.04 g cm -3 is obtained from the experimental coexistence curve using the linear-diameter rule. The estimates of F c obtained from our simulation data are lower by 13-25%. According to Guggenheim, the reduced surface tension), where M r denotes the molar mass and c a constant, is supposed to be a universal function of the reduced temperature T/T c for all pure fluids. While many nonpolar, weakly polar, and moderately polar liquids adhere to this principle of corresponding states, deviations from Guggenheim's master curve are seen for strongly polar, hydrogen-bonding substances and for simple inorganic molten salts, such as NaCl and KCl. We find that, despite its ionicity, the data for [bmim][PF 6 ], both from experiment and from simulation, follow the master curve for at most moderately polar liquids, thereby indicating significant differences from the physicochemical properties of simple inorganic molten salts.

Measurements of the liquid-liquid phase diagrams of solutions of the ionic liquids (ILs) 1-dodecyl-3-methylimidazolium chloride (C12mimCl) in arenes (benzene, toluene, o-xylene, tetraline) and 1-tetradecyl-3-methylimidazolium chloride (C14mimCl) in CCl4 are reported and compared with those of solutions of trihexyl-tetradecyl-phosphonium halides (P666 14Cl, P666 14Br) in hydrocarbons and 1-alkyl-3-methylimidazolium tetrafluoroborates (CnmimBF4) in alcohols and water. The phase diagrams of solutions of tetrapentyl-ammonium bromide (N5555Br) in water and KI in SO2 are also discussed. Except for the KI/SO2 system, which features a lower critical solution point (LCSP), all systems have an upper critical solution point (UCSP) and show corresponding-states behavior. The experimental data are compared with results from simulations and theory concerning the model fluid of charged hard spheres in a dielectric continuum, termed restricted primitive model (RPM). The analysis in terms of of RPM variables shows agreement with the location of the critical point (CP) of the model with noticeable systematic deviations. However, for protic solvents, the CP becomes an LCSP, while in aprotic solvents the CP is a UCSP as expected for Coulomb systems. This indicates that in aprotic solvents, the phase transition is essentially determined by the Coulomb interactions, while in the solutions in protic solvents with hydrogen bonds, both Coulomb and solvophobic interactions are important.

Molecular dynamics simulations of the liquid−vapor interface of aqueous solutions of sodium fluoride and of sodium iodide have been carried out using nonpolarizable force fields for ions and water molecules. Despite the absence of explicit polarizability, the tendency of iodide ions to show an enhanced concentration at the surface that was reported for polarizable force fields (Jungwirth, P.; Tobias, D. J. J. Phys. Chem. B 2001, 105, 10468) is reproduced, while sodium and fluoride ions prefer the interior of the bulk liquid. These observations are confirmed by the contributions of the different species to the surface potential. The systems we study here are much larger than the ones investigated in previous simulations by other authors, which enables us to calculate the adsorption of ions at the interface from the density profiles and subsequentlyvia Gibbs’ adsorption isothermthe corresponding excess surface tension over that of pure water. The so-obtained values for the surface tension are compared with the results calculated directly from the normal and lateral components of the pressure tensor in the simulation. Consistency is found among the data, but the directly obtained values have significantly larger error bars and are intrinsically more scattered. The Gibbs adsorption isotherm thus not only is a thermodynamic requirement to be met but also offers a reliable and less error-prone way of calculating the surface tension increment from density profiles.