The thermodynamics of molecules with discrete potentials

Fluids formed by molecules interacting with discrete potentials are examined in the context of perturbation theory and the reference hypernetted chain equation (RHNC) solution to the Ornstein—zernike equation. A perturbation theory for discrete-potential fluids (DPT) is presented, which only requires one to know the properties of a square-well fluid of variable range. Several potentials are studied: square-shoulder, a combination of a square-well and square-shoulder, and a discrete representation of a continuous potential model. We have found that the DPT approach reproduces the RHNC predictions in most of the cases.     

Thermodynamics of micellization of C7 and C8 lecithins

The surface tensions of the lecithins diheptanoyl- and dioctanoylphosphatidylcholine in phosphate medium, pH 7.4, have been measured over the temperature range 288.15–313.15K. Critical micelle concentrations, thermodynamic micellization parameters, adsorption parameters, transfer data of micelles to the aqueous surface and surface area minima per molecule were obtained from these measurements. Critical micelle concentrations slightly decrease with temperature. The micellization processes became increasingly exothermic with increase in temperature. The variation of Gibbs energies of transfer indicates that the processes are most favourable at low temperatures. From a study of entropy-enthalpy compensation phenomenon a compensation temperature of 300^?1 K^?1 was found, and from the intercept an analysis of the hydrophobic-hydrophilic balance was carried out.     

A density functional study of plutonyl trifluoroacetone complexes in the gas phase and in solution

The results of a density functional study on a plutonyl compound with two trifluoroacetone ligands are presented. Several conformations of the complex have been examined, namely the structure in which the two ligands are in a cis conformation one with respect to the other, in a trans conformation one with respect to the other, and the structure in which the two ligands lie on the same plane. The calculations have been carried out at the local density approximation level of theory. The relative energies of the conformers have been determined and their geometries have been optimized in the gas phase and in an organic solution. The liquid-state environmental effects are included via a simple cavity model and by using the self-consistent reaction field method. This study shows that the trends in stability of the different conformers in the gas and liquid phases are similar and that the most stable conformer has a cis structure.     

Perturbation theory for mixtures of discrete potential fluids

A thermodynamic perturbation theory for mixtures of fluids composed of particles interacting via discrete potentials is presented, based on previous work for pure component systems. Square-well and square-shoulder mixtures are accurately described by this theory, giving the necessary information for studying a wide range of discrete potential fluids. As an example of this, the theory is applied to a discrete Lennard-Jones mixture, obtaining very good results when compared against computer simulation values. The scope of this work is to implement perturbation theory for discrete potential systems in modern theories for complex fluids.     

Determination of the Rate Constant of the Reaction of CCl2 with HCl

The rate constant of the reaction between CCl₂ radicals and HCl was experimentally determined. The CCl₂ radicals were obtained by infrared multiphoton dissociation of CDCl₃. The time dependence of the CCl₂ radicals' concentration in the presence of HCl was determined by laser‐induced fluorescence. The experimental conditions allowed us to associate the decrease in the concentration of radicals to the self‐recombination reaction to form C₂Cl₄ and to the reaction with HCl to form CHCl₃. The rate constant for the self‐recombination reaction was determined to be in the high‐pressure regime. The value obtained at 300 K was (5.7 ± 0.1) × 10^?13 cm³ molecule^?1 s^?1, whereas the value of the rate constant measured for the reaction with HCl was (2.7 ± 0.1) × 10^?14 cm³ molecule^?1 s^?1.