Advances in Molecular Relaxation and Interaction Processes最新文献

It is shown that the definition of a mutual viscosity between solvent and solute can both give information about the structure of the solution and explain the discrepancy between the viscosity of the solvent and the correlation time of the solute. As the viscosity is connected with the friction coefficient, its unambiguous determination is of great significance for the calculation of the relaxation time.

The temperature dependence of the ultrasonic velocity and ultransonic damping as well as the hypersonic velocity and relaxation time τ_v1 was measured in liquid cyclohexane by Brillouin scattering. These data suggest a two-step relaxation process for the vibrational relaxing specific heat. According to the results at low temperature all but the two lowest vibrational modes, at high temperature all but the three lowest vibrational modes, are contributing to the specific heat of the first relaxation step. The relaxation time τ_v2 of the second step was calculated based on the bulk viscosity derived from the Brillouin line width. For the non-relaxing fraction of the bulk viscosity the corresponding values of Argon and Krypton using the theorem of the corresponding states were applied.

Finally the collision number Z₁₀ necessary for the deactivation of the lowest vibrational mode was evaluated on the basis of both the hard sphere model and the cell model. According to the Slawsky-Herzfeld theory a linear relationship between In Z₁₀ and T^−1/3 was found for both models.

Dielectric relaxation measurements on NH---N bonded complexes of pyrrole and indole with pyridine and quinoline molecules respectively have been undertaken at a 9.8 GHz frequency over a range of temperatures 293 –323 K by use of the method of Gopala Krishna[1], Higasi[2] and Higasi, Koga and Nakamura [3]. The observed results indicate the presence of NH---N bonded complexes in the above temperature range under the microwave field. The dipole moments associated with the complexes and thermodynamical parameters have also been determined, and the results obtained exhibit formation of NH---N bond, which behave as a single unit under the applied field.

The kinetics of complexation at 25°C of nickel malonate in water-glycerine mixtures has been studied by the pressure-jump relaxation technique. For the water-glycerine mixtures, the ratio k_f/K_F, (namely the ratio between the forward rate constant k_f and the pre-equilibration constant for the bimolecular diffusion step K_F), shows a decrease within a factor of two from pure water to 49% glycerine in water. This decrease, if significant, is at variance with the apparently random scatter of the same data for water-fructose mixtures. In order to decide whether these changes in k_f/K_F reflect solvation of nickel ion, or modification of the chelation mechanism, the complexation of Ni(NCS)₂ at 10°C in the same solvent of composition 49% glycerine has been studied. It is proposed that the changes in k_f/K_F, may be caused by the changes in the K_F with solvent composition, namely with changes in the ion-pair distance rather than with changes in the reaction mechanism. This is reflected in the constancy of the k_f's with solvent composition.

Some Fokker/Planck/Kramers equations of current interest are solved numerically for autocorrelation functions and spectra. It is demonstrated that uncritical use of these equations should be avoided because of the neglect of memory effects inherent in their make-up. Only in the case discussed by Evans (1976) does this type of equation produce realistic spectra, and then only over a limited range of temperature and viscosity. The way to proceed in problems involving molecular diffusion of this type is to use molecular dynamics simulation

The kinetics of formation of iron(III) monochelates with glycolic and lactic acids have been investigated by the temperature-jump method at 25.0°C and ionic strength 1.0 M over the acidity range 0.0200 – 0.900 M. The kinetic data indicate that two reaction paths, involving the FeOH²⁺ ion and the neutral and anionic (HL-L⁻) forms of the ligands, lead to the iron(III) chelate formation and that the monodentate complex Fe(OH)L-LH⁺ is formed as an intermediate compound. Moreover the observed [H⁺]-dependence of the forward rate constants permits us to estimate the contribution of intermediate steps to the limiting rate in the overall chelate formation process.

The overall consistency of experimentally available correlation times for liquid CH₂Cl₂ is tested with the aid of a new computer simulation at 293K lbar, using a 5 × 5 Lennard-Jones atom-atom potential with charges situated at the atomic sites. The various N.M.R. correlation times and the dielectric relaxation time are satisfactorily in line with the computer simulation. The infra-red correlation time reported by van Konynenberg and Steele is consistent with the simulation, but those reported by Rothschild are over 100 too short. The correlation time from depolarised Rayleigh scattering is over 3 times longer than the simulation result, and the neutron-scattering correlation time of Brier and Perry is about 100. shorter. The computer simulation reproduces the far infra-red spectrum of liquid CH₂Cl₂ fairly well and is therefore considered to be reliable.

A coordinated project, such as the EMLG Delta Project is needed to improve the overall consistency of these basic features of liquid phase molecular dynamics, exemplified by liquid CH₂Cl₂.