Infrared fluorescence and double infrared resonance have been used to measure the V-T relaxation of CD3F and CD4 in mixtures with He, Ne, Ar, Kr, Xe and HCl in the gas phase and in the liquid Ar, Kr, Xe. It is shown that the temperature dependence of V-T probabilities in the interval 350–150°K can be attributed to an increasing influence of long range forces. In the mixture CD3F + HCl, where H-bonded complexes CD3F…HCl have been formed, the vibrational relaxation rate considerably increases with decreasing temperature. It is found that the probabilities of V-T energy transfer in cryogenic solutions are lower than those measured in the gas phae.
Empirical formulae for evaluating the dielectric relaxation intensity, or the magnitude of dielectric dispersion, from dielectric loss data, proposed by Kita and Koizumi, in a limited range of frequency around the relaxation frequency for the Davidson - Cole relaxation has been verified in the case of three i-alkyl halides.
In transient relaxation method studies of fast reactions, if the rate of response of the chemical system is comparable with that of the perturbation, the exact shape of the forcing function must be taken into account in the kinetic treatment of the relaxation response. An analysis of the transient response of multiple coupled equilibria using Laplace transform is presented for various forms of step or impulse perturbation. The method enables one to calculate the relaxation amplitudes for an unrestricted number of coupled chemical equilibria. Various aspects of the analysis of the relaxation response are discussed.
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.
A molecular dynamics simulation of liquid CH2Cl2 is compared with the far infrared spectrum at the same state point (293K, 1 bar). Two representations of the force field are used, a 3×3 and 5×5 site-site interaction consisting of Lennard-Jones and charge terms. The far infra-red spectrum shows unambiguously that the 5×5 representation is more realistic in the sense that it reproduces the observed spectrum more closely.
The temperature dependence of the rotational diffusion in liquid CH2Cl2 has been measured in the far infrared from 10 to 220 cm−1 and 177K to 313K (f.p. to b.p. at 1bar). The results are interpreted at 177K and 293K with a molecular dynamics simulation using a 5 × 5 atom-atom potential with charge-charge electrodynamics. The simulation reproduces the basic features of the spectra but some experimental detail of the dependency of max, the far infrared peak frequency, on temperature is not followed by the simulation. The situation can be improved by accurately measuring the second dielectric virial coefficient βϵ of CH2Cl2 vapour in order to improve our knowledge of the intermolecular pair potential.
Large basis set Ab Initio calculations are reported for the variation of energy and electric dipole moment with internuclear separation for the diatoms ArHe and NeHe. Electron correlation effects are treated explicitly by the self consistent electron pairs method, and are found to be large. The effect of basis set superposition is examined, and found to be significant. Calculated potential well depths De and equilibrium internuclear separation Re compare with the εm and Rm values found by fitting various experimental data. The electric dipole moment pe for the ArHe diatom at distances ≈ RIe is larger than that for the NeHe diatom, in accordance with the fact that the full collision induced absorption spectrum has been observed experimentally only for the latter. The variation of pe with R shows fine structure at R ≈ Re not previously reported.
The real component of shear impedance, RL, was measured in concentrated aqueous solutions of sodium deoxycholate, by means of different experimental techniques, in the frequency range 30KHz – 830MHz, at temperatures from 20°to 40°C. The results obtained give direct confirmation on the existence of viscoelastic effects in such a system; they allow, also, to evaluate an upper limit for the dynamic shear viscosity values. From these data it is evident that shear viscosity relaxes well below the usual frequency range of longitudinal ultrasonic experiments. As a consequence, the previously observed large longitudinal ultrasonic absorption appear to be due mainly to volume viscosity contributions.
A new skewed-arc alternative to the Davidson-Cole permittivity function is derived. It has the same very low and very high frequency limit angles in its Cole-Cole arc and approaches the behavior of the Davidson-Cole permittivity function for small values of the exponent parameter β. The difference, however, becomes increasingly appreciable for large values of β. The distribution function g(ln τ) is very much like that for the Davidson-Cole system, but it does not exhibit any singular nor discontinuous slope behavior for any value of the relaxation time τ.
Le calcul de la “densité spectrale” I(ω) pour le modèle de dispersion diélectrique de type Davidson et Cole traduit bien la distribution asymétrique des temps de relaxation. En effet, il n'y a plus de relation linéaire entre le produit ωI(ω) et l'absorption diélectrique ε″. L'étude expérimentale effectuée sur la série des amines primaires (propylamine à dodécylamine) justifie pleinement les calculs théoriques développés. On peut ainsi obtenir des informations complémentaires sur leur processus de relaxation.
Calculs des energies totales, distributions de charge electronique, energies orbitales, moments dipolaires et quadripolaires pour cyclopropane, HCN et leur complexe a liaison hydrogene
Some aspects of the difficulties encountered in describing irreversible phenomena by means of classical mechanics are considered.
Pair potentials and polarizabilities of LiBr, NaBr, KBr and Br22− have been computed over a range of internuclear separations R using the gaussian orbital SCF-MO method. Together with results previously reported for all other ion pairs, the present values form a complete and consistent set of energy and polarizability data on the bromides of lithium, sodium and potassium.
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.
The dielectric absorption of seven aliphatic straight chain aldehydes has been examined in a polystyrene matrix between 80 and 325 K and in the 50 to 105 Hz region. For each solute two sets of absorption curves were found, one around 100 K and the other in approximately the 200 – 300 K region. The relaxation data for the 100 K region has been identified with segmental rotation and probably, with rotation about the C CHO bond as well. The higher temperature process, which involves relaxation of appreciably larger units, may well be an overlap of molecular and larger segmental rotation. n-Nonanal was examined in a polystyrene and a polypropylene matrix and in both cases gave low and high temperaure absorption curves. The parameters for the former were almost independent of the medium whereas those for the latter process exhibited considerable variation.
The heats of dilution of ternary aqueous solutions of urea and alcohols have been determined at 25°C. From the experimental data the values of the excess enthalpies HijE and of the pair enthalpy interaction coefficients hij have been evaluated and compared with the data reported in the literature. The values of the hij coefficients at 25°C are all positive and depend on the length and branching of the alkyl chain of the alcohols. The results are discussed in terms of the effects of a chaotropic agent”, as urea, on the cospheres of mainly hydrophobic such as alcohols.
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 kf/KF, (namely the ratio between the forward rate constant kf and the pre-equilibration constant for the bimolecular diffusion step KF), 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 kf/KF 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 kf/KF, may be caused by the changes in the KF 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 kf's with solvent composition.
L'influence de la complexation sur la vibration ν(CH) a été étudiée dans les complexes R2CHOH…Y (R = CF3; CD3 ; Y = base) ; elle dépend de la conformation de la molécule d'alcool. Quand le groupement CH est transpar rapport au groupement OH, les abaissements de ν(CH) dans la complexation sont proportionnels á ceux de ν(OH) ; pour les formes gauches, la relation entre'les abaissements de ν(CH) et ceux de ν(OH) dépend de R et pour R = CF3 elle dépend aussi de la basicité de Y. On met ainsi en évidence le caractère directionnel de la délocalisation électronique dans la liaison hydrogène. I1 n'y a pas d'influence notable de la complexation sur les intensityés des bandes νCH). Une liaison C-H…Y a été envisagée pour rendre compte de la solvatation des complexes (CF3)2CHOH…Y par les bases Y.
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.
