Advances in Molecular Relaxation and Interaction Processes最新文献

Large-scale gaussian orbital SCF-MO results are reported for the title molecules. R_e(X…H) and D_e(X…H) values are given, and in either case the complexes OC…HF and DC…HCl are more stable than the corresponding CO…HX complexes. The changes on electronic distribution on complex formation are discussed in terms of Mulliken population indices.

The association between the acridinium orange cation and the fluorescein divalent anion in aqueous solution at pH = 8.0 was studied spectrophotometrically.

The experimental data allow to compute the association constants in the temperature range 3 – 40°C and to extimate the association enthalpy and the association entropy

The complex dielectric permittivity of methyl and ethylcellosolve at 25°C and in the frequency range 1–90 GHz are reported. The real and imaginary coefficients of the permittivity show a relaxation profile with frequency that can be interpreted either by a Cole-Davidson distribution function or by the sum of two discrete Debye-relaxation processes. Preference for the latter description is given not on the basis of an optimum of a numerical fit, but rather on the proposal that the two Debye processes are related to H-bond breaking, as for the alcohols, and to alkoxy and/or molecular tumbling respectively. Evidence of the above hypothesis is given by reporting the complex permittivity of methylcellosolve-dimethoxyethane mixtures in the whole composition range. It is shown that the relaxation contribution ε₀-ε_∞1, attributed to the lower Debye relaxation process (and assigned to the H-bond breaking process) is proportional to the molarity of methylcellosolve up to the pure liquid. This shows that by substituting the OH group by the methoxy group, the effect attributed to (ε₀-ε_∞1) decreases and disappears when no -OH groups are present as for pure dimethoxyethane. Further, by taking the position that the contribution ε₀-ε_∞1 is to be dealt with as in liquid mixtures, the apparent dipole moment μ∼3 Debyes is calculated by the Böttcher theory. This figure is comparable to the values of μ calculated by the Onsager theory for the alcohols. The above seems to suggest that although the Cole-Davidson distribution function may fit the relaxation profile numerically, it eludes (by its own nature) the molecular description of the dielectric relaxation processes.

In the review article the results of the adiabatic calorimetry, dielectric, nuclear magnetic resonance, quasielastic neutron scattering and X-ray investigations for four plastically crystalline compounds of the (CH₃)₃CX type (X = Cl, Br, NO₂ and CN) are presented. On this basis the intercorrelationships between the reorientational dynamics of the molecules and the molecular and crystal structures are discussed.

The three Raman A_l-bands of trichloromonosilanes HSiCℓ₃, DSiCℓ₃ are studied in the neat liquid state and in solution (isotopic dilution and inert solvent SiCℓ₄). The depolarization ratio ϱ is measured from the integrated strengths. The relaxation times τ_v and τ_2R are deduced from the corresponding correlation functions G_v(t) and G_2R(t).

Pure dephasing relaxation is predominant for the vibrational modes; the rotational relaxation appears to be of the diffusional type in SiCℓ4 and nearly free for the neat liquids at room temperature.

For two-component relaxation behaviour the time constant (apparent relaxation time) and the preexponential factor (apparent probability) of each of the components are complicated functions of the real relaxation times, the population fractions (real probabilities) and the lifetimes referring to two regions, between which an exchange of molecules, nuclei or spins occurs. The theoretical treatment of Zimmerman and Brittin is sketched and the apparent quantities as functions of the real quantities and vice versa are plotted in detail.

The infrared spectra of 10 substituted pyridines with trifluoroacetic acid-d₁ were examined in dry benzene and benzene-d₆ with respect to the mass effect on the AH stretching vibration. The isotopic frequency ratio of the gravity centres, V̄_o^H/ V̄_o^D, varies between 1.04 and 1.19. The isotopic frequency ratio, together with the previously described solvent effect on the chemical shift of hydrogen bonded protons, possibly indicates an expansion of the

A new method (justified by permittivity measurement) is proposed to study dielectric relaxation by means of the interface air-dielectric response.

The characterization established here for a single relaxation (the distribution of relaxation times is represented by a Dirac function) can be used when a generalization is wanted for more complex cases (symmetric or asymmetric distribution function of relaxation times).

Application of this method to a series of mono-substituted benzenes is shown in this paper.