Photoionization and ab initio study of Ba(H2O)n (n = 1-4) clusters

An experimental and theoretical study of the photoionization energies (IE's) of Ba(H(2)O)(n) clusters containing up to n = 4 water molecules has been performed. The clusters were generated by a pick-up source combining laser vaporization with pulsed supersonic expansion, and then photoionized by radiation of 272.5-340 nm. The experimentally determined IE(e)'s for n = 1 to 4 are 4.56 ± 0.05, 4.26 ± 0.05, 3.90 ± 0.05 and 3.71 ± 0.05 eV. This cluster size dependence of IE is reproduced within ±0.06 eV employing the mPW1PW91 density-functional and CCSD(T, Full) quantum-chemical methods combined with the 6-311++G(d,p) basis set for the H and O atoms and three different relativistic effective core potentials for Ba atoms. The calculations indicate that the lowest energy hydration structures represent the most relevant contributions to both the vertical and adiabatic ionization energies. Experimental and theoretical evidence correlates with the progressive surface-delocalization of the electron from the hydration cavity around the Ba atom and suggests that the intra-cluster electron transfer is possible even for small aggregates.     

Remarkable in vitro bactericidal activity of bismuth(iii) sulfonates against Helicobacter pylori

Four new tris-substituted bismuth(iii) sulfonates of general formula [Bi(O(3)SR)(3)] (R = phenyl 1, p-tolyl 2, 2,4,6-mesityl 3 and S-(+)-10-camphoryl 4) have been synthesised and characterised. Their synthesis by solvent-free (SF) and solvent-mediated (SM) methods has been explored and their activity against Helicobacter pylori has been investigated. The compounds 1-4 display a remarkable in vitro activity against three laboratory strains of H. pylori (B128, 26?695 and 251) with minimum inhibitory concentration (MIC) values as low as 0.049 μg mL(-1) for the strains B128 and 26?695, and 0.781 μg mL(-1) for the clinical isolate 251. This places most MIC values in the nano-molar region and demonstrates the strong influence of the sulfonate group on the bactericidal properties. The novel solid state structure [Bi(8)(O(3)SMes)(20)(SO(4))(2)(H(2)O)(6)]·(C(7)H(8))(7)5·(C(7)H(8))(7), derived from the SM reaction under reflux conditions, is presented and the incorporation of the two inorganic sulfate anions in the centre of the wheel-like bismuth sulfonate cluster explained.     

Ultrasound for low temperature dyeing of wool with acid dye

The possibility of reducing the temperature of conventional wool dyeing with an acid levelling dye using ultrasound was studied in order to reach exhaustion values comparable to those obtained with the standard procedure at 98 °C, obtaining dyed samples of good quality. The aim was to develop a laboratory method that could be transferred at industrial level, reducing both the energy consumption and fiber damage caused by the prolonged exposure to high temperature without the use of polluting auxiliary agents.Dyeings of wool fabrics were carried out in the temperature range between 60 °C and 80 °C using either mechanical or ultrasound agitation of the bath and coupling the two methods to compare the results. For each dyeing, the exhaustion curves of the dye bath were determined and the better results of dyeing kinetics were obtained with ultrasound coupled with mechanical stirring. Hence the corresponding half dyeing times, absorption rate constants according to Cegarra-Puente modified equation and ultrasonic efficiency were calculated in comparison with mechanical stirring alone. In the presence of ultrasound the absorption rate constants increased by at least 50%, at each temperature, confirming the synergic effect of sonication on the dyeing kinetics. Moreover the apparent activation energies were also evaluated and the positive effect of ultrasound was ascribed to the pre-exponential factor of the Arrhenius equation. It was also shown that the effect of ultrasound at 60 °C was just on the dye bath, practically unaffecting the wool fiber surface, as confirmed by the results of SEM analysis.Finally, fastness tests to rubbing and domestic laundering yielded good values for samples dyed in ultrasound assisted process even at the lower temperature. These results suggest the possibility, thanks to the use of ultrasound, to obtain a well equalized dyeing on wool working yet at 60 °C, a temperature process strongly lower than 98 °C, currently used in industry, which damages the mechanical properties of the fibers.     

Electrochemical Au deposition on stepped Si(1 1 1)-H surfaces: 3D versus 2D growth studied by AFM and X-ray diffraction

In order to grow magnetic layers on silicon substrates, a non-magnetic buffer layer is often needed to avoid silicide formation and to reproduce the perpendicular magnetic anisotropy obtained on metal single crystals, as in the case of Co on Au(1 1 1) and Pt(1 1 1). In this context, we have studied the electrochemical growth of Au buffer layers, and show that it is possible to obtain different film morphologies on hydrogen-terminated vicinal Si(1 1 1) surfaces by varying the electrochemical deposition parameters and solution composition. Two different morphologies have been obtained as observed by atomic force microscopy: continuous 2D Au films (chloride solution at pH 4), and films consisting in flat top 3D Au islands decorating the Si(1 1 1) step edges (cyanide solution at pH 14). X-ray diffraction measurements reveal that the gold layer and islands have Au(1 1 1) orientation and are in epitaxy with the Si(1 1 1) surface. In the case of islands, the lateral facets have also Au(1 1 1) orientation. Results are discussed within a model in which the breaking of the Si-H surface bonds plays a major role in the Au nucleation and growth mechanisms.     

π-He interactions at T=106 MeV

interactions at have been studied by means of a self-shunted streamer chamber filled with helium at atmospheric pressure. This technique allowed reconstruction of the complete kinematics of the nuclear events under analysis, since tracks of slow p, α, tritium and ³He are readily measurable. The study revealed that the ⁴He nucleus behaves as a Planck radiator, emitting a Planck-like spectrum of high energy γs, when hit by a π beam of . A resonant behaviour in the π⁻n invariant mass spectrum has been observed, with and in the neutron knockout reaction: we consider this to be the first experimental evidence for the existence of the Δ⁻. The observed mass shift and width narrowing are compatible with the activation of an isobaric collective resonance in the ⁴He nucleus. The collaboration has also observed a resonant behaviour in the π⁻pp invariant mass spectrum in the pp double-charge-exchange reaction, on nuclear photoemulsion, compatible with the activation of the J^P=0⁻d^′ dibaryonic resonance with a strong p-p final state interaction. A new direct measured upper limit for the ν_μ mass has been derived by measuring a complete decay π-μ-e event recorded at the CERN PS179 experiment (Ne scattering): at a 90% confidence level, .     

Internal energy content of n-butylbenzene, bromobenzene, iodobenzene and aniline molecular ions generated by two-photon ionization at 266 nm. A photodissociation study

A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd.     

Kinetics and mechanism of the reaction of CF3 radicals with NO2

The reaction of CF₃ with NO₂ was studied at 296 ± 2K using two different absolute techniques. Absolute rate constants of (1.6 ± 0.3) × 10⁻¹¹ and (2.1 _−0.3⁺⁰⁷) × 10⁻¹¹ cm³ molecule⁻¹ s⁻¹ were derived by IR fluorescence and UV absorption spectroscopy, respectively. The reaction proceeds via two reaction channels: CF₃ + NO₂ → CF₂O + FNO, (70 ± 12)% and CF₃ + NO₂ → CF₃O + NO, (30 ± 12)%. An upper limit of 11% for formation of other reaction products was determined. The overall rate constant was within the uncertainty independent of total pressure between 0.4 to 760 torr. © 1996 John Wiley & Sons, Inc.     

Subthreshold inclusiveη production in nuclei by 1 GeV protons

The doubly differential cross-section for theη production in the reactionp + A → X + η has been measured on⁶Li, C, Al, Cu, and Au targets using a proton beam of 1 GeV kinetic energy of the Saturne protosynchrotron in Saclay.η mesons were detected by a two arm neutral meson spectrometer, PINOT. TheA dependence of the doubly differential production cross-section is provided and is compared to theoretical predictions.     

The IR multiphoton decomposition of CF3I. The effect of inert and reactive gases

The multiphoton decomposition of CF₃I with a pulsed CO₂ laser has been studied at incident fluences of 0.6 and 1.2 J/cm². The effect of pressure on the reaction probability for dissociation of CF₃I was measured in the presence of added isobutane, Ar and CO₂. In the experiments with isobutane, the CF₃ radicals generated by the decomposition of excited CF₃I react to yield CF₃H in competition with the recombination to C₂F₆. The laser absorption cross section was also measured as a function of fluence at a pressure of 0.1 torr of CF₃I and with 0.5–2.0 torr of added isobutane. The experimental results were modeled with a master equation in order to obtain information on the energy transferred by collisions of excited CF₃I with the bath molecules. An energy dependent value of 〈ΔE〉_d produces the best fit to the experimental data. Integration of the rate equations to account for the fractional product yield, [CF₃I]/[C₂F₆], allowed for the calculation of the specific rate constant for hydrogen abstraction from isobutane by CF₃ radicals. The value obtained is dependent on the total pressure and higher than expected at room temperature. From these results, an effective temperature for the reaction mixture was calculated. © 1994 John Wiley & Sons, Inc.     

Dehalogenation of α -haloketones and vic-dibromides with nickel boride

α-Haloketones and $\text{vic}$-dibromides are converted to the corresponding ketones and alkenes respectively with nickel boride generated $\text{in situ}$ from sodium borohydride and nickel chloride.