Advances in Molecular Relaxation and Interaction Processes最新文献

The interaction between carbonyl bases (benzophenone, acetophenone and cyclohexanone) and HCl or HBr has been studied by infrared spectrometry in the 3500 - 800 cm⁻¹ range. In carbontetrachloride, the four studied bases form with HCl normal hydrogen bonds of 1:1 and 1:2 (one base - two acids) stoichiometry. This is also the case for the adducts of benzophenone and acetophenone with HBr. The formation constants are reported. For the interaction between acetone and HBr, the concentration of protonated species seems to be very weak. The interaction between cyclohexanone and HBr leads to complexes of 1:1 and 2:1 (two bases - 1 acid) stoichiometry. The appearance in the spectrum of a broad absorption band between 1500 and 800 cm⁻¹ suggests the formation of nearly symmetrical (OHO)⁺ hydrogen bonds. The infrared spectra in dichloromethane and in binary solution are also discussed.

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.

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.

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.

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

The permittivity and dielectric loss of 2-chloro-6-methyl aniline, 3-chloro-2-methyl aniline, 3-chloro-4-methyl aniline, 4-chloro-2-methyl aniline and 5-chloro-2-methyl aniline have been measured at four microwave frequencies viz., 33.45, 18.98, 9.945 and 1.80 GHz and also at 300 KHz and optical frequency at 35°C in benzene solution. Ther permittivity and dielectric loss at different frequencies have been plotted against concentration (wt. fraction). The slopes of these straight lines have been used for the complex plane plots (a″ Vs. a′). The complex plane plots for these compounds are Cole-Cole arc's. The most probable relaxation time (τ_o) and distribution parameter (α) have been evaluated from these plots. The values of these parameters are found to be in agreement with those obtained from Higasi's single frequency method. Data have also been analysed in terms of two relaxation processes i.e., corresponding to overall rotation and group rotation. Nearly equal values of τ₂, the relaxation time for intramolecular rotation, for these substituted anilines suggest that the amino-group relaxes by an inversion mechanism. The dipole moments, evaluated by the microwave method, are also reported.