Structural and vibrational analysis of the OH torsional motion in difluorohydroxyborane

In this work, we present a complete structural and vibrational analysis of the OH torsional motion in difluorohydroxyborane (BF₂OH) at the HF/aug‐cc‐pVTZ, MP2(full)/aug‐cc‐pVTZ, and CCSD/aug‐cc‐pVTZ theory levels. After full relaxation of the geometry, the equilibrium structure is found in a planar conformation of C_s symmetry. The difference in the two BF distances suggests the existence of a nonbonded interaction between the fluorine and oxygen atoms. The structural and energetic variation of BF₂OH as a function of the OH torsional angle is considered. The torsional barrier, at the CCSD/aug‐cc‐pVTZ level, and including the effect of the zero‐point energy of the remaining vibrations, is found 2,728 cm^?1. In addition, an anharmonic Hamiltonian for the OH torsional mode is presented and variationally solved. To simplify the treatment and to classify the energy levels, BF₂OH is classified under a G₄ nonrigid group accounting for the inversion symmetry of the molecule and the interchange of the fluorine atoms. The computed torsional energy levels exhibit a very small inversion splitting. The torsional spectrum is simulated considering the dipole moment components along the principal axes of inertia as an explicit function of the torsional coordinate. We observe three dominant bands in the spectrum formed by doublets corresponding to ν₉ = 0 → 1, 2 transitions. The fundamental is an a‐type, Franck–Condon, transition. This is the strongest and appears at 466.80 cm^?1 with relative intensity 0.4312. The ν₉ = 0 → 2 bands correspond to doublets of b‐ and c‐type, i.e., Herzberg–Teller transitions. These are two overlapping bands found at 890.92 and 890.94 cm^?1 with intensity 0.2207 for the b‐type band and 0.2193 for the c‐type band. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2011     

Spectrophotometric determination of zinc and copper in a multi-syringe flow injection analysis system using a liquid waveguide capillary cell: application to natural waters

This work exploits a multi-syringe injection analysis (MSFIA) system coupled with a long liquid waveguide capillary cell for the spectrophotometric determination of zinc and copper in waters. A liquid waveguide capillary cell (1.0 m pathlength, 550 μm i.d. and 250 μL internal volume) was used to enhance the sensitivity of the detection. The determination for both ions is based on a colorimetric reaction with zincon at different pH values. The developed methodology compares favourably with other previously described procedures, as it allows to reach low detection limits for both cations (LODs of 0.1 and 2 μg L⁻¹, for copper and zinc, respectively), without the need for any pre-concentration step. The system also provided a linear response up to 100 μg L⁻¹ with a high throughput (43 h⁻¹) and low reagent consumption and effluent production. The developed work was applied to natural waters and three certified reference water samples.     

Persistent non-ergodic fluctuations in mesoscopic insulators: The NSS model in the unitary and symplectic ensembles

We give a detailed picture of the mesoscopic conductance fluctuations in the deep insulating regime (DIR) within the Nguyen, Spivak and Shklovskii model in the unitary and symplectic ensembles. Slutski's theorem is invoked to rigorously state the ergodic problem for conductance fluctuations in the DIR, in contrast with previous studies. A weakly decaying behavior of the log-conductance correlation function, even weaker when spin-orbit scatterers are included, is established on the relevant field scale of the model. Such a slow decay implies that the stochastic process, defined by the fluctuations of the log-conductance, is non-ergodic in the mean square sense in the ensembles with the reported symmetries. The results can be interpreted in terms of the effective number of samples within the available magnetic scale. Using the replica approach, we derive the strong localisation counterparts of the well known 'cooperon' and 'diffuson' which permit analyzing quantitatively the decaying behavior of the correlation function and reveal its symmetry related properties in agreement with the numerical results. Received 11 April 2002 / Received in final form 27 August 2002 Published online 19 November 2002     

Stability of LaNiO3 gas diffusion oxygen electrodes

In this work LaNiO₃ perovskite-type oxide, prepared by a self-combustion method, was optimized for activity and stability as an anode material for water electrolysis. A full electrochemical study was conducted in order to kinetically characterize electrodes prepared using carbon paper as a base for porous gas-diffusion electrodes in alkaline media, regarding water oxidation and oxygen reduction reactions at room temperature. An electrode stability study was performed by potential cycling and at constant current density, using cyclic voltammetry and electrochemical impedance spectroscopy to check on stability after cycling with complementary scanning electron microscopy/energy dispersive X-ray spectrometry (SEM/EDS) analysis of fresh and degraded electrodes. Comparison was made using nickel foam as a support for LaNiO₃ deposition. Carbon instability in the potential region of interest contrasted with the lower contact resistance between the oxide and support of the Ni foam. Higher metal oxide loadings and dimensional stability were also possible.     

Determination of mercury in fish by cold vapor atomic absorption spectrophotometry using a multicommuted flow injection analysis system.

A flow system was developed for the determination of total mercury concentration in fish samples by cold vapor atomic absorption spectrophotometry (CVAAS), based on the multicommuted flow injection analysis (MCFIA) approach. The system uses independently controlled solenoid valves for the introduction of reagents and samples. When not injected, solutions were recirculating to the reservoir bottles, in this way reducing the waste produced by the analytical system and also the sample consumption. Results were compared to those obtained by the reference flow injection procedure. Accuracy was also assessed by recovery studies using a certified reference material as well as spiked samples; recovery percentages in the range of 90.7% to 99.8% were found. The repeatability of the method was better than 6.0% (RSD, n = 10). A limit of detection of 4.8 microg of mercury per kg of fresh fish sample was achieved. The total waste produced was reduced to 30% of that from the reference flow injection CVAAS procedure.     

Direct introduction of slurry samples in multi-syringe flow injection analysis: determination of potassium in plant samples.

The present work explores the slurry sampling approach for automatic, flow-based plant analysis. For this purpose, pinch valves were introduced into a multi-syringe flow injection analysis manifold to provide the repeatable aspiration of a few microliters of plant suspension before the material was further processed through the flow system. For validation of the proposed approach, the determination of potassium by flame emission spectrometry was implemented. Several parameters were studied: the concentration of plant particles in the sample suspension and the utilization of matrix modifiers. Microwave digestion was also implemented; no significant difference was found when certified reference material was analyzed with or without the in-line digestion step. The system was successfully applied to 13 samples within a concentration range of 2.5 to 100 mg g(-1). A determination frequency of 28 h(-1) was achieved and the precision was better than 4.0% (n = 12).     

New hybrid method for reactive systems from integrating molecular orbital or molecular mechanics methods with analytical potential energy surfaces

A computational approach to calculating potential energy surfaces for reactive systems is presented and tested. This hybrid approach is based on integrated methods where calculations for a small model system are performed by using analytical potential energy surfaces, and for the real system by using molecular orbital or molecular mechanics methods. The method is tested on a hydrogen abstraction reaction by using the variational transition-state theory with multidimensional tunneling corrections. The agreement between the calculated and experimental information depends on the quality of the method chosen for the real system. When the real system is treated by accurate quantum mechanics methods, the rate constants are in excellent agreement with the experimental measurements over a wide temperature range. When the real system is treated by molecular mechanics methods, the results are still good, which is very encouraging since molecular mechanics itself is not at all capable of describing this reactive system. Since no experimental information or additional fits are required to apply this method, it can be used to improve the accuracy of molecular orbital methods or to extend the molecular mechanics method to treat any reactive system with the single constraint of the availability of an analytical potential energy surface that describes the model system.     

The influence of aniline and its derivatives on the corrosion behaviour of copper in acid solution

The inhibiting action of aniline and its derivatives on the corrosion of copper in hydrochloric acid has been investigated, with emphasis on the role of substituents. With this purpose five different anilines were selected: aniline, p-chloro aniline, p-nitro aniline, p-methoxy and p-methyl aniline. The electrochemical and gravimetric results, obtained in the absence and presence of different concentrations of inhibitors, revealed that aniline reduces the corrosion of copper, with a critical concentration of 10^–2 M. Furthermore, the interaction energy calculated as G_ads gave a value of 4.2 kcal mol^–1 indicating physisorption of the organic compound at the copper surface. The results have also shown that substituents, either electron donors (–CH₃, –OCH₃) or, electron acceptors (–NO₂, –Cl) in para position, decrease the inhibition action of aniline. A theoretical study using molecular mechanic and ab initio Hartree Fock methods, to model the adsorption of aniline on copper (100) showed results in good agreement with the experimental data. Aniline adsorbs parallel to the copper surface, showing no preference for a specific adsorption site. On the other hand, from ab initio Hartree Fock calculations, an adsorption energy between 2 kcal/mol and 5 kcal/mol is obtained, which is close to the experimental value, confirming that the adsorption of aniline on the metal substrate is rather weak. In view of these results, the orientation of the aniline molecule with respect to the copper surface is considered to be the dominant effect.     

Hydrophilization of PVC Surfaces by Argon Plasma Immersion Ion Implantation

Commercial polyvinylchloride (PVC) sheets were treated by plasma immersion ion implantation, PIII. Samples were immersed in argon glow discharges and biased with 25 kV negative pulses. Exposure time to the bombardment plasma changed from 900 to 10,800 s. Through contact angle measurements, the effect of the exposure time on the PVC wettability was investigated. Independent of t, all samples presented contact angles, , equal to zero after the treatment. However, in some cases, surface hydrophilization was not stable, as revealed by the temporal evolution of . Samples bombarded for shorter periods recovered partially or totally the hydrophobic character while the one exposed for the longest time stayed highly hydrophilic. These modifications are ascribed to the Cl loss and O incorporation as shown by XPS measurements. Furthermore, the mobility of surface polar groups and the variation in the cross-linking degree can also affect the PVC wettability.     

Potentiometric multi-syringe flow injection system for determination of exchangeable potassium in soils with in-line extraction

A multi-syringe flow injection system for the potentiometric determination of exchangeable potassium in soil samples is proposed. Firstly, a manifold was devised to allow determination in soil extracts prepared off-line. It was possible to analyze samples prepared in extractants with different composition (Mehlich or Morgan) without physical or chemical modification of the manifold. A linear dynamic concentration range of 6–391 mg L^− 1 was obtained, allowing the direct introduction of soil extract without dilution. A determination frequency of 50 h^− 1 was achieved, with good repeatability for 10 consecutive injections of soil extracts (RSD < 3.0%). The in-line preparation of soil extract was implemented by automatic addition of extractant solution to a previously weighed portion of soil, followed by in-line filtration. Good repeatability was attained as the variance of the extraction procedure was not significantly different from the variance obtained in consecutive measurements of the same extract. Furthermore, results comparable to those obtained by off-line extraction and determination by flame emission spectrometry were attained for the two soil samples tested. Using this procedure, a determination frequency of 13 h^− 1 and a sampling rate of 4 h^− 1 were achieved.