The Ni + O2 reaction: a combined IR matrix isolation and theoretical study of the formation and structure of NiO2

The reaction of Ni atoms with molecular oxygen has been reinvestigated experimentally in neon matrices and theoretically at the DFT PW91PW91/6311G(3df) level. Experimental results show that i) the nature of the ground electronic state of the superoxide metastable product is the same in neon and argon matrices, ii) two different photochemical pathways exist for the conversion of the superoxide to the dioxide ground state (involving 1.6 or 4 eV photons) and iii) an important matrix effect exists in the Ni + O(2)--> Ni(O(2)) or ONiO branching ratios. Theoretical results confirm that the electronic ground state of the metastable superoxide corresponds to the singlet state, in agreement with former CCSD(T) calculations, but in contradiction with other recent works. Our results show that the ground electronic state of the dioxide is (1)Sigma(+)(g) with the lowest triplet and quintet states at slightly higher energy, consistent with the observation of weak vibronic transitions in the near infrared. The potential energy profiles are modelled for the ground state and nine electronic excited states and a pathway for the Ni(triplet) + O(2)(triplet) --> Ni(O(2)) or ONiO (singlet) reaction is proposed, as well as for the Ni(O(2)) --> ONiO photochemical reaction, accounting for the experimental observations.     

Photoelectrolysis of water with semiconductors

The use of semiconductors, as photoelectrodes in electrolytic cells for the electrolysis of water, is described and the results reported in the literature for various semiconductors are reviewed. The most important properties of the semiconductor are shown to be the band-gap energyE _g , and the flat-band potentialU _fb . The semiconductor absorbs photons that are more energetic than the band-gap energy and creates electronhole pairs. These charge carriers can be separated before recombination by the electric field at the semiconductor-electrolyte interface. For electrolysis to proceed, the potential corresponding to the band gap must appreciably exceed the standard potential for the electrolysis of water, 1.23 volts. In addition, the flat-band potential must be more negative than the hydrogen potential or an external bias voltage is required. The semiconductor must not corrode under the operating conditions and must permit transfer of the minority carrier to the electrolyte. The current theories of charge transfer and reaction mechanism are discussed. Many semiconductive oxides have been tested as photoanodes and found to be stable. However, only those compounds that have band gaps of ca. 3 eV have been found to have flat-band potentials that are more negative than the hydrogen potential. These compounds will electrolyse water, without additional bias voltage, but are inefficient absorbers of solar energy. Experiments withp-type photocathodes,p andn combinations and various special configurations are also described. The paper concludes with a general discussion of the practical prospects of photoelectrolysis in comparison with solid-state solar cells.     

Nanosized Shape‐Changing Colloids from Liquid Crystalline Elastomers

A method to prepare shape‐changing nanospheres from liquid crystalline elastomers is reported. The nanosized colloids are prepared by a miniemulsion process. During this process, colloids are prepared from a liquid crystalline (LC) main‐chain polyester and subsequently crosslinked into a nanometer‐sized LC elastomer. The ability of these LC elastomers to change their shape at the phase transition temperature from the smectic A to the isotropic phase was detected by temperature‐dependent transmission electron microscopy. The phase transition‐induced shape change leads to strongly shape anisotropic nanosized elastomer particles.

     

Trilocal structures. IV. momentum-dependent tree functions

Enlarging the set of tree functions to include those which depend on the momentum vector has the effect of introducing new families and subfamilies of functions. Four auxiliary conditions are used in the generation of these functions. These auxiliary conditions introduce, as eigenvalues, four parameters in terms of which the coefficients of the momentum-dependent functions can then be expressed as linear combinations of the 16 leading coefficients. These 16 are all rest-system coefficients. Thus the momentum-dependent part of the expansion is expressible in terms of the rest-system portion, using only these four parameters.     

Pesticide residue analysis of a dietary ingredient by gas chromatography/selected-ion monitoring mass spectrometry using neutral alumina solid-phase extraction cleanup

A sample cleanup procedure has been developed to remove coextractives that interfere with pesticide residue analysis of a dietary ingredient (Product B), an extract consisting of Scutellaria baicalensis and Acacia catechu. Samples were extracted using 1% acetic acid in acetonitrile, followed by solid-phase extraction and analysis by capillary gas chromatography with mass spectrometry in the selective-ion monitoring mode. Neutral alumina (alumina N) was found to be the most effective sorbent to remove coextractives from Product B; other materials that were tested but failed to remove interference were graphitized carbon black/primary-secondary amine (PSA), octadecylsilane (C18), Florisil, Oasis MCX, and strong anion exchange-PSA. The method was specifically developed for Product B, which was spiked with 41 organochlorine and organophosphorus pesticides, and resulted in the recovery of 80 to 120% at U.S. Pharmacopeia limits (0.06 to 4 microg/g) for the majority of the pesticides.     

Awakening of a ferrous complex's electronic spin in an aqueous solution induced by a chemical stimulus

A low-spin, macrocyclic iron(II) complex in an aqueous solution responds to the addition of a chemical reactant (dithionite) by transformation into a high-spin complex, detectable by measurement of the longitudinal relaxation time (T(1)) of surrounding water hydrogen nuclear spins. The initial compound does not modify T(1) of pure water at concentrations as high as 4 mM. The response is pH-dependent, and the complex is robust at a variety of conditions.     

Coulomb damping

Viscous damping is commonly discussed in beginning differential equations and physics texts but dry friction or Coulomb friction is not despite dry friction being encountered in many physical applications. One reason for avoiding this topic is that the equations involve a jump discontinuity in the damping term. In this article, we adopt an energy approach which permits a general discussion on how to investigate trajectories for second-order differential equations representing mechanical vibration models having dry friction. This approach is suitable for classroom discussion and computer laboratory investigation in beginning courses, hence introduction of dry friction need not be delayed for more advanced courses in mechanics or modelling. Our method is applied to a harmonic oscillator example and a pendulum model. One advantage of this method is that the values of the maximum deflections of a solution can be calculated without solving the differential equation either analytically or numerically, a technique that depends on only the initial conditions.