Advances in Molecular Relaxation and Interaction Processes最新文献

The influence of a.c. electric field (5kHz) on the IR and FIR spectra of the nematic phase of some liquid crystals with strong positive dielectric anisotropy ( ε_a≈ 10 – 20) and weak negative dielectric anisotropy(ε_a≈ −0,2 – 0,7) was investigated. The changes in the half-widths and integral intensity are explained by means of the changes in the molecular orientation due to the electric field influence.

The basis of the method has been presented in part I (preceeding paper in this issue) together with the results on propanol, pentanol and decanol at 25°C. This second part is devoted to propanol-decanol mixtures in several fractions in volume and concludes with a general discussion where the molecular mechanisms responsible for the three dielectric dispersion regions of the pure primary alcohols are pointed out.

SCF-MO results using a large gaussian sp-basis set are given for the hydrogen-bonded complexes of cyclopropane with HF and HCl. The complexes are calculated to have edge-on geometry, as found experimentally. Well depths, Mulliken population indices and one-electron properties are given for the complexes.

To analyse the dielectric relaxation spectra of some pure normal alcohols and their binary mixtures, the experimental time domain techniques (T.D.S.) in conjunction with a deconvolution procedure combined with powerful numerical minimization methods are shown to be useful.

The results on propanol, pentanol and decanol at 25°C are given. Those concerning propanol-decanol mixtures will be presented in the next paper with a general discussion in conclusion.

Experimental results of a flash photolysis study of bromo cresol green and thymol blue are presented. They give further support to the recently proposed complex mechanism: A photoinduced rotational isomerization is followed by two consecutive proton transfer reactions and, occasionally, by an intermediate sultone ring closure.

Electrostatic molecular potential approach is used to determine reaction channels for Me₃N·AlH₃ and Me₃N·AlCl₃. Predictions concerning reactivity of these complexes are formulated.

When the complex X-H…O(H)CH(CD₃)₂ in a carbon tetrachloride solution is formed between a proton donor XH and isopropanol(D₆), we observe for the ν(CH) wavenumber of isopropanol(D₆) an increase of about 15 to 45 cm⁻¹ which depends on the proton donor ability of XH ; we also observe a decrease for the ν(OH) wavenumber of about 13 to 21 cm⁻¹. The ν(OH) anharmonicity is unchanged. When the CH group is at a greater distance from the hydroxyl group [in the (CF₃)₃COH…O(H)CD₂CD₂H complex] the increase for $\text{ν}$(CH) is only 3 cm⁻¹. The ν(OH) wavenumber for the free hydroxyl group in the homomolecular linear dimer of isopropanol(D₆) is 5 cm⁻¹ lower than the observed value for the monomer. The intensity of the ν(CH) band generally decreases in the complexation, that of the ν(OH) band is slightly modified, or increases when the proton donor is perfluorotertiobutanol.

The processes of formation and of relaxation of molecular exciplex in solution are discussed in the framework of method which incorporates solvent parameters into calculations of potential energy curves of different states attainable by exciplex system. An analysis of the results of calculations shows that intramolecular vibrations are serving as acceptors for energy dissipated by the system in the formation process and that this accepting ability can be modified by solvent polarity. It is also shown that the most important role is played by solvent in the relaxation of encounter complex to “equilibrium” exciplex.

A “molecular dynamics” computer simulation of liquid CH₂Cl₂ and CHCl₃ has revealed a time dependence of the simple kinetic energy correlation function 〈v²(O)J²(t)〉/(〈v²(O)〉〈J²(O)〉) where $\text{v}$ is the c. of m. linear velocity and $\text{J}$ the molecular $\text{angular}$ momentum. This is constant at unity for all t in conventional analytical theory, which is therefore in need of development. The variates $\text{v}$ and $\text{J}$ are not Gaussian during the approach to equilibrium.

IR spectra of HCl complexes with acetonitrile, olefins have been studied and also for the comparison of methanol polymers in solutions of liquefied Xe, Kr, Ar and N₂.

The half-width of the band for HCl complexed with acetonitrile in liquid Kr is 35 cm⁻¹ at 165 K; this is half of that value in Xe at the same temperature and an order of magnitude lower than in standard solvents. Temperature narrowing of this band down to 30 cm⁻¹ has been found on cooling the solution to 120 K. The temperature shift of HCl bands in complexes of moderate strength not referring to self-association was observed. The results obtained are in agreement with the representation of a hydrogen-bonded system as an underdamped ahnarmonic stochastic oscillator.