Band 219, Heft 8

The study of intermolecular forces has been of increasing interest in the past. New theoretical and experimental techniques have been developed which allow an improved understanding of these important interactions. We will give an introduction to the theoretical concepts of the description of intermolecular forces. We will tackle Ar–CO as prototype system of intermolecular forces which has been subject of intensive experimental and theoretical work in the past and has evolved to one of the most investigated intermolecular complexes. We will give here an overview over the numerous theoretical and experimental studies which have been published in the literature. A comparison between the most recent ab initio studies and the experimental work demonstrates a lack of sufficient agreement. We have carried out a semi-empirical fit of the potential energy surface to five of the seven known intermolecular modes. All modes could be reproduced within 0.4 cm using our new potential energy surface. The most significant deviation which was found in comparison to previous ab initio potentials was the appearance of a second local minimum in the potential energy surface. These results indicate a lack of a sufficient accurate theoretical description of intermolecular forces for this “little beast” which remains still a challenge for the future.

It is shown that the difference between the heat of chemical reaction derived by the Van't-Hoff equation, Δ H 0 , and measured by calorimetry, Δ Q 0 , is P Δ V 0 .

Molar conductances of Bu 4 NBPh 4 , Bu 4 NClO 4 , Bu 4 NI, Bu 4 NBr, Bu 4 NCF 3 COO, Pr 4 NBr, Et 4 NI, Et 4 NBPh 4 , NaClO 4 , NaBPh 4 , [Cu(CH 3 CN) 4 ]ClO 4 and CF 3 COOAg have been measured in the concentration range (1–120) × 10 −4 mol dm −3 in acetonitrile (AN) and binary mixtures of AN with n -butyronitrile ( n -BTN) and DMA. The conductance data in all cases have been analyzed by the Shedlovsky method to evaluate Λ o and K A of these electrolytes. Some of these salts are associated in these solvent systems. Ion-association in case of silver (I) salts is the largest and relatively more in case of AN + DMA mixtures. Limiting ion conductances (λ i o ) and hence actual solvated radii ( r i ) in all solvent systems have been evaluated using a modified form of Stoke's law. Cu + , Ag + and Na + are highly solvated, CF 3 COO − , ClO 4 − , Br − and I − are poorly/moderately solvated and tetraalkylammonium ions (R 4 N + ) and Ph 4 B − are not solvated in AN + n -BTN and AN + DMA mixtures.

The influence of the hindered reorientations of CCl 3 groups on the decay of NQR spin echo signals has been investigated. In contrast to the well known literature approaches to the solution of this problem we do not use the perturbation theory of Bloembergen, Purcell and Pound. (PACS codes: 76.60.-k; 76.60.Gv; 76.60.Lz)

The catalytic oxidation of benzyl alcohol has been carried out by using dioxygen as oxidant in the presence of Fe(acac) 3 (acetyl acetone)/1,10-phenanthroline/base system in toluene at 80°. Oxygen was activated successfully by the Fe-catalyst and oxidized benzyl alcohol to benzyl aldehyde in ∼100% selectivity. It was found that the oxidation of benzyl alcohol was very sensitive to water in this reaction system, and small amount of water could obviously decrease the reactivity. Based on the results of cyclic voltammetry and ESR, a binuclear-Fe mechanism was also proposed.

Vapor pressure p of LiI + C 2 H 5 OH solutions at T = (298.15 to 323.15) K were measured by the static method. The osmotic Φ and activity coefficients γ and activity of solvent a s have been evaluated. The experiments were carried out in molality range m = (0.34523 to 8.61859) mol kg −1 . The Antoine equation for the empiric description of experimental vapor pressure results and the Pitzer–Mayorga model with inclusion of Archer's ionic strength dependence of the third virial coefficient for the description of calculated osmotic coefficients were used. The parameters of Archer extended Pitzer model was used for evaluation of activity coefficients.

Standard partial molar volumes V 2,Φ 0 , viscosity B -coefficients and molar conductivities λ m for the ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate [C 4 mim][PF 6 ] in aqueous ethanol solutions ( x ethanol = 0.5∼0.9) have been determined from density, viscosity and conductivity measurements at 298.15 K. It is shown that values of V 2,Φ 0 decrease, while those of viscosity B -coefficients increase with increasing mole fraction of ethanol in the solvents. The molar conductivities of the ionic liquid are found to be decreased with increase of both the ionic liquid concentration and the ethanol content in the systems. Experimental results have been discussed in terms of the ionic liquid–solvent interactions and the ion associations of the ionic liquid in aqueous ethanol solutions.

The thermal decomposition kinetics of [Co(bipy)(H 2 O) 4 ](C 4 H 4 O 4 ) · 4H 2 O was carried out by thermogravimetry (TG) and derivate thermogravimetry (DTG) analysis at four heating rates of 5, 8, 11 and 14 °C/min in nitrogen atmosphere. TG confirmed that thermal decomposition of the compound takes place in a single step. The kinetic parameters (activation energy, frequency factor, and activation entropy) were calculated using various forms of non-isothermal methods. The activation energy obtained by the Ozawa method is in agreement with the value determined by the Coats–Redfern technique. However, a much lower activation energy was obtained by the Kissinger method.

A method based on classical physics, utilizing the first few even moments of the polarized and depolarized interaction-induced light scattering spectra at room temperature to derive an empirical model for the pair-polarizability trace and anisotropy of interacting atoms, with adjustable free parameters, is described and applied to the spectra of krypton. Good agreement with ab initio and analytical results in the literature is obtained and profiles calculated with our empirical models are in excellent agreement with experiments. Theoretical calculations using these models are compared with the experimental values of the second dielectric constant and second virial Kerr coefficient for this gas. The results show excellent agreement with the experiments.

Recently, we found that for a simple first-order reaction having equilibrium constant equal to 1, the amplitudes of equilibrium fluctuations can be, on the discrete time scale (scale of reaction events), satisfactorily described using the random walk approximation for the distribution and mean amplitude of fluctuation having the fixed lifetime 2 r reaction events. Below, we propose another characterization of fluctuations in the random walk introducing an averaged trajectory of fluctuations and suggest another formula for the mean amplitude of fluctuations having a fixed length. The results are used in characterization of equilibrium fluctuations of first order reversible chemical reaction having the equilibrium constant equal to 1.