Calculations on transitions in singly- and doubly-excited C IV

Wavelengths for transitions in the quartet spectrum of C IV are calculated and compared with recent experimental measurements. Transition probabilities and radiative lifetimes are also predicted for several of the lowest 1s 2snl ⁴ L and 1s2pnl ⁴ L levels up toL=4. In addition, wavelengths and transition probabilities for some recently observed C IV doublet transitions to then=4 level are presented.     

Electronic transitions in C60 and its ions

The electronic spectrum of C₆₀ is calculated using quantum mechanical methods. The first allowed transition in C₆₀ is calculated at an energy of 3.5 eV and with an oscillator strength of 0.09. Several transitions are found at higher energies with comparatively strong oscillator strengths, the strongest one being at 5.78 eV (λ=214 nm). The calculated energy level diagram of C₆₀ is also used to predict wavelengths for transitions in C ₆₀ ⁺ and C ₆₀ ^? . A comparison is made with some recently observed diffuse interstellar bands at 1180 nm and 1320 nm, which have been speculated to originate from C ₆₀ ⁺ .     

Fulvalene ions—I: Calculations on calicene ions

Calculations on planar and 90°-twisted calicene and the mono- and di-ions derived from it are reported. Both all-valence-electron and π-electron calculations were performed, utilizing an “all aromatic” geometry throughout. Calculated ionization energies indicate that there should be no appreciable gain in resonance stabilization upon radical formation, however the radicals should be amenable to preparation. Good general agreement was obtained between the π-electron charge and spin distributions predicted by the INDO and PPP methods. In addition, these are generally in good agreement with simple predictions based on Hu¨ckel's (4n + 2) rule.     

Phase transitions and the stability of atomic and molecular ions

Quantum phase transitions at absolute zero temperature can take place as some parameter in the Hamiltonian of the system is varied. For such transitions, crossing the phase boundary means that the quantum ground state changes in some fundamental way. For the Hamiltonian of N-electron atoms, this parameter is taken to be the nuclear charge. As the nuclear charge reaches a critical point, the quantum ground state changes its characters from being bound to being degenerate or absorbed by a continuum. We describe here a method to calculate the critical nuclear charge for which an atom can bind an extra electron to form a stable negative ion. The estimate of the critical nuclear charge will be used to explain and predict the stability of atomic negative ions. The method can be generalized to predict the stability of molecular negative ions. A detailed calculation for the critical parameters for two center molecular ions is also included.     

Metal complex formation with dicarbonyl-ligands. Calculations on glyoxal complexes with alkali and alkaline earth metal ions

Ab initio MO SCF calculations on the complexes of Li, Na, K, Be, Mg and Ca ions with glyoxal have been performed. These calculations represent the first part of a series of theoretical investigations on the dependence of complex formation properties of ligands containing two carbonyl groups on the structure of the cordinative center. Special attention has been paid to the chelate effect, which is found to increase with increasing atomic number within the series of ions. The calculated values are compared with our recent data obtained from UV spectroscopy of ion complexes with dicarbonyl ligands.     

Reactions of gaseous ions. I. Methane and ethylene

At elevated pressures in a mass spectrometer ion source reactions occur between certain ions and the neutral species present. We have studied the various secondary ions formed in methane and ethylene at elevated pressures and have determined the reactions by which they are formed and the rates of these reactions. The rates are all extremely fast. The reaction rates have been treated by classical collision theory and it has been shown that to a fair approximation the cross-sections and reaction rate constants can be predicted from a simple balance of rotational and polarization forces. [Reprinted from J. Am. Chem. Soc. 1957; 79: 2419.] Copyright 1957 by the American Chemical Society and reprinted by permission of the copyright owner.     

Calculations on the π→1π* transitions in large conjugated carbonyl compounds using the molecules-in-molecules method

Assignments of the ^1* electronic transitions in large carbonyl compounds have been carried out using the molecules-in-molecules method.     

Vibronic intensities in centrosymmetric lanthanide complex ions. I

Summary A theoretical model to calculate the vibronic intensities induced by the odd vibrational modes in centrosymmetric lanthanide complexes is developed and applied to octahedral complex ions, LnX ₆ ^3– , such as occur in the hexachloroelpasolites Cs₂NaLnCl₆. Both the crystal field and the ligand polarisation contributions are evaluated using a standard set of symmetry coordinates. For the crystal field term a truncated expansion of the intermediates states is employed rather than the more conventional closure approximation. Special care is necessary to ensure that the phases of the contributions are correctly determined since the cross-term between the ligand polarisation and crystal field contributions is signed. General equations applicable to anyf ⁿ complex ion are derived and an example of their application to the PrCl ₆ ^3– ion is given The agreement with experiment is satisfactory.     

On the nature of mesophase transitions in polymers I. The isotropic-nematic transition

The purpose of this study is to examine the application of the meander model to the understanding of transition properties in the isotropic-nematic (paper I), and in the isotropic-smectic or — lamellar (paper II) phase transitions in polymers. This paper deals with the phase transitionwithin the stable meander structure which will take place if the entropy of cube rotation is counterbalanced by a reduction of interfacial energy that may be realized by a parallel arrangement of the anisotropic meander cubes within the coarse grains (i/n-transition). But no change in the short-range order within the cubes will be assumed. Considering the free energy in the meander model, the only relevant term for this transition is g _rot which is derived, minimized to equilibrium, and discussed. By this procedure, the transition temperature, the heat and volume of transition, as well as their temperature dependences are deduced. The most important parameter is the excess volumev _e per chain of cube side length, caused by crossed-chains at the cube-interfaces, which can be determined by atomistic calculations. This model theory is compared with experimental data [15] on one low molecular weight LC and two LC side chain polymers, as well as on the hypothetici/n-transition of polyethylene.Dedicated to Prof. H. H. Kausch on the occasion of his 60th birthday.     

Low-temperature phase transitions in (C5H5NH)Ag5I6

The solid electrolyte (C₅H₅NH)Ag₅I₆ undergoes two low-temperature transitions, probably associated with the ordering of the pyridinium ions. The two phases are monoclinic and have structures closely related to that of the hexagonal phase at 240°K. The transition to the γ-phase at 230°K is second order, and that from the γ- to the δ-phase at 180°K, first order. In the γ-phase, the monoclinic a and b axes correspond to the orthohexagonal B and A axes, respectively; in the δ-phase, the correspondence is reversed. If the pyridinium ions order in the γ-phase, its space group is most probably Cc. If the pyridinium ions are ordered in the δ-phase, the N atoms must lie on twofold axes in $\text{C2}\text{c}$, but the space group Cc is also possible for this phase.     

13C NMR spectroscopy of copoly(arylenephthalide) derivatives with diphenyloxide and terphenyl fragments in the main chain

¹H and ¹³С NMR spectral assignments have been provided for low‐molecular reference monomers, poly(diphenyleneoxidephthalide) and periodic copoly(arylenephthalide) derivatives such as AB, ABB, and ABBB (where A = terphenylenephthalide and B = diphenyleneoxidephthalide) using ¹H‐¹H COSY, ¹H‐¹³C HSQC and HMBC NMR techniques. Distinctive ¹³C NMR chemical shifts of a main chain have been observed containing fragments of similar structures and lateral phthalate groups being part of various diads. Copyright © 2013 John Wiley & Sons, Ltd.     

Mechanical behaviour of isotactic polypropylenes in the lower and the upper glass transitions ranges

 The effects of physical ageing on both glass transitions of isotactic polypropylenes (homopolymer and random copolymer)are investigated by isothermal dynamic mechanical spectroscopy and by low strain creep. The ageing-time dependent expressions of the amorphous fractions which undergo each relaxation are introduced in a rheological model composed by a modified Zener model (associated to the β-relaxation) in series with a γ-element (associated to the α-relaxation). The agreement between the responses of this model and the creep and dynamic results is good over a time (or frequency) range covering up to 15 decades for three kinds of isotactic polypropylenes. Received: 2 January 1996 Accepted: 16 August 1996     

Endor investigation of the biphenyl and terphenyl anion radicals in solution

From the ENDOR spectra of the mononegative ions of biphenyl and ortho-, meta- and para-terphenyl in solution complete sets of hyperfine splitting constants could be determined. The splittings are interpreted in terms of SCF MO spin densities obtained from McLachlan type calculations. It turns out that π-σ spin delocalization effects do not play a significant role in the spin density distribution in these radicals although some of them deviate considerably from coplanarity.     

Spectrophotometric studies on the interactions of C.I. Basic Red 9 and C.I. Acid Blue 25 with hexadecyltrimethylammonium bromide in cationic surfactant micelles

Interactions between cationic dye-cationic surfactant and anionic dye-cationic surfactant systems were investigated in aqueous solutions using spectrophotometric method at 288.15, 298.15, 308.15 and 318.15 K. C.I. Basic Red 9 (BR9) and C.I. Acid Blue 25 (AB25) were used as cationic and anionic dyes, respectively, and hexadecyltrimethylammonium bromide (HDTMABr) was selected as cationic surfactant in this study. Although there was an interaction between the AB25 and the HDTMABr molecules, an interaction between the BR9 and HDTMABr did not occur due to the electrostatic repulsion forces. Binding constants and partition coefficients between the micellar and the bulk water phases for the AB25-HDTMABr system were calculated from the changes in absorbance values and the critical micelle concentrations at different temperatures. It was found that the values of binding constant and partition coefficient decreased with increasing temperature. Thermodynamic parameters (ΔG⁰, ΔH⁰ and ΔS⁰) were determined for the binding and partition processes of AB25-HDTMABr system. It was concluded from ΔG⁰ values that the binding of AB25 to HDTMABr occurred spontaneously. In addition, the binding and partition processes were exothermic.     

Calculations of induced moments in large molecules I. Polarizabilities and second hyperpolarizabilities in some alkanes

We report the results of coupled Hartree-Fock computations for the average polarizability, , and hyperpolarizability, , of CH₄, C₂H₆, C₃H₆ and C₃H₈. The Hamiltonian matrices are constructed from an extended CNDO model. Small as well as large basis sets were tested. Agreement with available experimental values is within 13% for and 31% for .     

Interaction of ions with phosphatidylcholine and phosphatidylethanolamine at the n-heptane/water interface: I. Inorganic ions

Electrocapillary phenomena at the n-heptane/water interface in the presence of phosphatidylcholine or phosphatidylethanolamine in alkane were studied by the drop-volume technique. The regulating role of the electric field was established in phospholipid interaction with inorganic ions: changes in interfacial pressure at the n-heptane/water interface with addition of electrolytes were observed only when an electric field was applied to the system of two immiscible liquids. It is suggested that ions can penetrate and bond by phospholipid functional groups at the phase boundary only after reorientation of the latter in the electric field. As in the case of ionic surfactants, change in interfacial pressure was directly proportional to the cube root of the concentration of electrolyte. It is assumed that as a result of preferential binding by phospholipid functional groups of ions of one sign, lipid molecules are charged and at the phase boundary behave themselves like ionic surfactants. Experiments with salts of multicharged ions, La³⁺, [Fe(CN)₆]³⁻, and [Fe(CN)₆]⁴⁻, have shown that mainly phospholipid functional groups bind cations.     

Thioketone spectroscopy: An analysis of the lower electronic transitions in thioacetone and thioacetaldehyde

Visible and ultraviolet spectra of the unstable species, thioacetaldehyde, CH₃CHS, thioacetone, (CH₃)₂CS, and thioacetone-d₆ have been studied in the gas phase. The valence n → π* excitations, Ã ← X? and ã ← X?, have been identified. Rydberg n → 4s, 4p_y and 4p_z and π → π* valence excitations have been found in thioacetone. In thioacetaldehyde a Rydberg-valence interaction mixes the n,4s and π,π* states which leads to a broad absorption of mixed character between 200 and 220 nm.     

Influence of anion-induced adsorption on D.C. polarography of metal ions

Some adsorption isotherms for anion-induced adsorption of metal ions are proposed. The influences of adsorption on d.c polarograms are examined theoretically. The consequences for the determination of stability constants from polarographic data are discussed.