Reactive resonances in the photodissociation of symmetric triatomic molecules: an interpretation of collinear CO2 in terms of polar coordinates

We discuss the origin of reactive scattering resonances in absorption cross sections following the collinear photodissociation of symmetric triatomic molecules. The analysis of spectra for CO₂ dissociation, previously calculated by Kulander and Light, becomes very simple in terms of polar coordinates. Of particular interest is a symmetry effect which is not observable in ordinary scattering calculations.     

A coupled states reactive scattering study of bending excited resonances in three-dimensional H + H2

Reaction probabilities from coupled states calculations on the Liu-Siegbahn-Truhlar-Horowitz surface for H+H₂ are calculated for the energy range 0.90–1.30 eV. Peaks in the vibrationally inelastic reaction probabilities near 1.10, 1.20 and 1.22–1.24 eV suggest that bending excited resonances labelled by the quantum numbers (11¹0), (12⁰0) and (12²0) exist.     

Interference effects in the electrical conductivity tensors of doped polar semiconductors

In this paper, we develop a general procedure, based on the Kubo formula, for finding the frequency- and wavevector-dependent electrical conductivity tensor for arbitrary polarizations of the applied electric field. This procedure gives careful consideration to both the electron and the ion contributions to the current density. We find that, in addition to the standard electron and ion contributions to the conductivity tensor, there are contributions arising from the quantum interference between the electrons and the ions. These interference effects, which will affect the infrared absorption of a material, are similar to the interference effects observed by Cerdeira, Fjeldly, and Cardona (Solid State Commun.13 (1973), 325–328; Phys. Rev. B8 (1973), 4734–4745; 9 (1974), 4344–4350) in Raman scattering from p-type Si. We then evaluate these cross terms for simple models of a variety of semiconductors. We find that these interference effects are finite-q effects, with the actual dependence of the cross terms on the wavevector q being sensitive to the symmetry of the crystal. We also find that, in principle, these cross terms may be quite large near the TO-phonon frequency ω_TO. The cross terms are evaluated for both n-type and p-type semiconductors, and it is suggested that they are probably most important for p-type materials. However, we also find that the basic structure of these terms is very similar in the two cases.     

Evaluation of substituted polycarbonates and a blend with polystyrene as gas separation membranes

The balance between the rate and the selectivity of transport of various gas pairs in a series of polycarbonates has been examined. Replacement of the four available hydrogens on the aromatic rings of the bisphenol-A unit with CH₃, Cl, or Br groups gives materials with a better balance of these two characteristics than the unsubstituted polycarbonate (PC). For example, using CH₃ substitution increases the permeability to O₂ by nearly a factor of four with no loss in O₂/N₂ selectivity compared with PC, while using Br substitution increases O₂/N₂ selectivity by 50% without any loss in O₂ permeability compared with PC. While these substitutions affect the permeability through both its mobility and solubility components, the remarkable selectivity effects are caused primarily by changes in relative mobility since the changes in solubility characteristics are nearly the same for all gases. These substitutions alter chain motions, cohesion, and packing as discussed. The tetramethylbisphenol-A polycarbonate forms miscible blends with polystyrene. These blends show absolute permeability coefficients which are lower than additivity while the selectivity of transport is greater. These effects are a result of the interactions between the two polymers.     

Proton-ionizable crown compounds : 5. Macrocycle-mediated proton-coupled transport of alkali metal cations in H2OCH2Cl2H2O liquid membrane systems

Alkali cation transport is studied using proton-ionizable macrocycle carriers of the 4-hydroxypyridine and pyridone types in a bulk H₂OCH₂Cl₂H₂O liquid membrane system as a function of source and receiving phase pH. A pyridone crown-6 type macrocycle containing an octyl substituent (3) transports Li⁺, Na⁺, K⁺, Rb⁺ and Cs⁺ from MOH solutions by a proton-coupled mechanism in which no co-anion is transported. In these cases, alkali cation transport increases exponentially with increasing source phase pH above pH 12. Generally, alkali cation transport at source phase pH 14 is higher when nitric acid is present (receiving pH = 1.5) than when it is absent. In competitive transport experiments with macrocycle 3 involving K⁺) and one other alkali cation M⁺, K⁺ is transported selectively over M⁺ by 4.6 (Na⁺), 2.7 (Rb⁺) and 6.3 (Cs⁺) fold when the source and receiving phase pH values are 14 and 7, respectively.     

Synthesis and electrical properties of Vanadyl(V)chloride complexes of N-2(4,5,6-monosubstituted pyridyl)-N′-aryl substituted thioureas

VOCl₃ formed six-coordinated complexes with N-aryl-N′-2(4,5,6-mono-substituted pyridyl)thioureas of the general formula [VOCl₃(RNHCSNHR′)], where R = pyridyl, 5-nitropyridyl, 4-methylpyridyl, 6-methylpyridyl groups and R′ = —C₆H₅, o-C₆H₅(CH₃) and p-C₆H₄(CH₃). The complexes have been characterized by means of elemental analysis, molar conductance, magnetic susceptibility, IR, UV—VIS, and ¹H NMR spectral data. The thermally stimulated depolarization effect was studied in samples polarized under different conditions. The results indicate two distinct transitions in the temperature range 92–100°C and 120–125°C for the ligands, whereas the VOCl₃-complexes show no breaks. The polarization—depolarization phenomena were correlated with the physicochemical changes occurring in the matrix. Depolarization kinetic data such as activation energy (E_a) and relaxation time (τ) of the electrets are reported.     

The dimerization of diphenyl(cyclopentadienyl)phosphine ligands by Diels-Alder addition

Reaction of diphenyl(cyclopentadienyl)phosphine, 1, with [PdCl₂(PhCN)₂], [PtCl₂(SMe₂)₂] or [M(CO)₄(norbornadiene)], where M = Mo or W, gave the complexes [PdCl₂{(Ph₂P)₂C₁₀H₁₀}], [PtCl₂{(Ph₂P)₂C₁₀H₁₀}] or [M(CO)₄{(Ph₂P)₂C₁₀H₁₀}] respectively, in which the ligand underwent dimerization by Diels-Alder addition. The reaction occurs in a very selective way and this is rationalized in terms of a template effect, in which two ligands 1 in mutually cis positions undergo the Diels-Alder reaction. In contrast, the complex [Fe(CO)₄(Ph₂PC₅H₅)] is stable to Diels-Alder addition. The structures of the complexes were deduced by ¹H, ¹³C and ³¹P NMR spectroscopy. The major product contains a six-membered chelate ring while a minor product, formed in the palladium and platinum systems only, contains a five-membered chelate ring.