Use of non-aqueous electrochemical cells to investigate air- and water-sensitive hydrogen storage materials

Electrochemical methods have been used to study hydrogen in vanadium, titanium and three binary magnesium alloy systems. These materials are all sensitive to air and/or water, which prohibits the use of aqueous electrolytes. The measurements have involved the use of alkali halide and lower temperature organic-anion molten salts saturated with an alkali hydride so that they conduct charge by the transport of hydride ions, rather than protons. Alkali metals, or their alloys, can be used as indirect reference electrodes for hydrogen in these electrolytes.     

The relation between the Gibbs phase rule and reference electrodes

Reference electrodes play an important role in the study of many aspects of electrochemical systems. Experimental work in the literature often involves the use of different reference systems, and it is sometimes difficult to translate between measurements made with one from those made using another. This situation is made even worse by the fact that reference electrodes that are used in solid state electrochemical systems are based upon the potentials of electrically neutral chemical species. On the other hand, the general practice in aqueous electrochemistry is to use reference electrodes that involve the properties of ions. Examples are discussed of the translation between reference states based upon neutral species on the basis of normal chemical thermodynamics. The identity and properties of the electrolyte plays no role. In aqueous systems the pH of the electrolyte becomes important in some cases, but not in others. These matters are discussed in terms of the Gibbs Phase Rule, showing the difference between zero-degree-of-freedom (ZDF) electrodes, and those in which an additional parameter, such as the electrolyte pH, must be specified. The interrelationship between these two types is illustrated using potential-pH plots, or Pourbaix diagrams. This provides a simple understanding of the glass electrode systems that are used to measure the pH of electrolytes. In electrodes with a mixed-conducting matrix and an internal ZDF reaction the potential is determined by the internal chemical reaction, rather than the external electrochemical reaction. Paper presented at the 5th Euroconference on Solid State Ionics, Benalmádena, Spain, Sept. 13–20, 1998     

Absence of bound states in extremely asymmetric positive diatomic molecules

It is shown that the Hamiltonian for a diatomic molecule consisting ofN electrons and two dynamic nuclei with chargesZ ₁ andZ ₂ has no bound states if one of the charges is sufficiently large. The nuclear motion is completely unrestricted, and the kinetic energy of both nuclei can be included in the Hamiltonian. One of the nuclear charges can be arbitrarily small, provided that the other is sufficiently large.Research supported in part by NSF grant DMS-8908125     

Study of the bidimensional state conformation of polyβ-benzyl-L-aspartate

Summary Huggins' theory of polymer monolayers, considered as bidimensional solutions is applicable to Poly-ß--benzil-L-aspartate films, obtained from two different spreading solvent: a pyridine free solvent and a 80% pyridine one.The spreading isotherms, deduced from the theory agree well with the experimental isotherm; therefore it is possible to deduce theoretical parameters showing the existence of two different macromolecular structures depending on the spreading solvent.In particular, if solvent is pyridine free, it appears that the monolayers have chain with -helix structure, if the solvent contains 80% pyridine they have chains with a more extended structure.

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Zusammenfassung Huggins Theorie der polymeren Monoschichten, als zweidimensionale Lösungen betrachtet, erweist sich als anwendbar auf Monoschichten von Poly--Benzyl-L-Aspartat, die man von zwei verschiedenen Spreitungslösemitteln erhält: ohne Pyridin oder 80% Pyridin enthaltend.Da die Übereinstimmung zwischen den experimentellen Spreitungsisothermen und den theoretisch erhaltenen gut ist, ist es möglich, Parameter abzuleiten, die geeignet sind, zwei verschiedene makromolekulare Strukturen je nach dem benutzten Spreitungslösemitteln zu charakterisieren.Insbesondere, wenn das Lösemittel kein Pyridin enthält, scheint es wahrscheinlich, daß die Monoschichten vorwiegend aus -Spiralen bestehen, wenn das Lösemittel Pyridin enthält, aus Ketten mit einer ausgedehnten Struktur.

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With 2 figures and 1 table     

Integrated Science and Mathematics Professional Development Programs

Over the past 5 years, integrated science and mathematics professional development programs for grades 4‐10 science and mathematics teachers have been designed and implemented at Wright State University. The primary goals of the programs were to enhance the science and mathematics content understanding and pedagogical knowledge of the participant teachers in order to increase teacher confidence and promote the implementation of standards‐based teaching practices in precollege classrooms. In this article, the general program structure developed and implemented over the years is discussed. Focusing on the 1999 program, evidence is presented of enhanced participant content understanding and pedagogical preparation, and specific examples of modified teacher practices are discussed.     

Theory of ionic transport in crystallographic tunnels

A model has been developed for the treatment of the motion of ions through crystallographic tunnels, as are found in materials that are interesting solid electrolytes. Consideration of both point charge and higher order attractive terms as well as overlap repulsion effects allows the calculation of the minimum energy positions of mobile ions and the activation energy barrier that they must surmount to move through the tunnel in the lattice. Calculations have been made for ions of different sizes in the AgI lattice which show that there is a set of minimum energy paths which do not follow the centerline of the tunnel, but deviate, periodically, with both direction and magnitude depending upon the cationic size. Also, in accordance with experimental observations, the activation energy for motion is smallest for cations of intermediate size, where the Coulombic, polarization, and repulsive contributions to the total energy are best balanced.     

Total synthesis of aigialomycin D: surprising chemoselectivity dependence on alkyne structure in nickel-catalyzed cyclizations

The total synthesis of aigialomycin D was carried out using a nickel-catalyzed ynal macrocyclization as a key step. This key step allowed macrocycle assembly and formation of a disubstituted alkene and a secondary hydroxyl stereocenter in a single step, although the stereocenter was formed unselectively. An interesting side reaction involving five-membered-ring synthesis by an aldehyde/styrene cyclization was observed when macrocyclization of an alkynyl silane was attempted. A mechanistic basis for this surprising process is provided.     

Rovibrationally selected and resolved pulsed field ionization-photoelectron study of propyne: ionization energy and spin-orbit interaction in propyne cation

By using a high-resolution infrared (IR) laser to prepare propyne (C(3)H(4)) in selected rotational levels of the excited nu(1) (acetylenic C-H stretching) vibration mode prior to vacuum ultraviolet (VUV) laser pulsed field ionization-photoelectron (PFI-PE) measurements, we have obtained rotationally resolved VUV-PFI-PE spectra for the C(3)H(4) (+)(X (2)E(32,12),nu(1) (+)=1) band. The analysis of these PFI-PE spectra leads to the determination of the spin-orbit constant of A=-13.0+/-0.2 cm(-1) for the C(3)H(4) (+)(X (2)E(32,12),nu(1) (+)=1) state. Using this A constant and the relative rotationally selected and resolved state-to-state photoionization cross sections thus measured, we have obtained an excellent simulation for the VUV-PFI-PE origin band of C(3)H(4) (+)(X (2)E(32,12)), yielding a value of 83 619.0+/-1.0 cm(-1) (10.367 44+/-0.000 12 eV) for the adiabatic ionization energy of C(3)H(4) [IE(C(3)H(4))]. The present two-color IR-VUV-PFI-PE study has also made possible the determination of the C-H stretching frequencies nu(1) (+)=3217.1+/-0.2 cm(-1) for C(3)H(4) (+)(X (2)E(32,12)). The spectral assignment and simulation were guided by high-level ab initio calculations on the IE(C(3)H(4)), Franck-Condon factors for photoionization transitions, and rotational constants and vibrational frequencies for C(3)H(4) (+).     

Assignment of rovibrational transitions of propyne in the region of 2934-2952 cm(-1) measured by two-color IR-vacuum ultraviolet laser photoion-photoelectron methods

The infrared (IR) spectrum of propyne in the region of 2934-2952 cm(-1) has been recorded by the IR-vacuum ultraviolet (VUV)-photoion method. The spectrum is shown to consist of two near-resonant, but noncoupled vibrational bands: the nu2 symmetric methyl C-H stretching vibrational band and a combination vibrational band nucs. The previously unobserved Q line of the nucs band is observed. The rotational transition lines of the nu2=1 band produces IR-VUV-pulsed field ionization-photoelectron (IR-VUV-PFI-PE) signal at the C3H4+ (nu2+=1) photoionization threshold. The rotational transition lines associated with the nucs band do not produce IR-VUV-PFI-PE signal. Rotational transition lines of both vibrational bands are assigned and simulated; and ab initio calculations further confirm the assignment.