The localized molecular orbitals for the hydration complexes of H+ and Li+ cations, F− anion, and linear dimer of water molecules are obtained from their CNDO/2 wavefunctions. The bonding of these systems is qualitatively discussed in the light of the localized orbitals.
Dielectric constants and losses have been measured at eight microwave frequencies between 1 and 35 GHz for 1-butanol and 1-decanol in paraffin oil and paraffin oil-n-heptane mixtures at 25 °C. The data have been analyzed in terms of two relaxation times and their dependence on viscosity and concentration is examined. The dielectric relaxation behaviour of these alcohols is not affected to any appreciable extent by increased macroscopic viscosity.
The decay of the transient birefringence induced by pulsed electric fields has been recorded and analysed for two different aqueous, polydisperse systems of rod-shaped particles. Attapulgite needles and asbestos fibres were the materials studied. The initial slopes of graphs of the logarithm of the normalised amplitudes during the decay process as a function of time were evaluated for both low and high electric field strengths. By comparing the data with those obtained from a simultaneous electron microscopic study, we verify the predictions of earlier theory from this research group that (i) discrete polydispersity average parameters are obtained from the initial slopes, (ii) from two such averages, which are quickly measured by this method, the sample polydispersity is indicated and (iii) the “peeling” method commonly used hitherto can give misleading size parameters.
The explicit expression for the relaxation spectrum of the polymerization reaction A1 + An ⇌ An+1 (n 1, 2, …) where all reactions are supposed to have the same values of the thermodynamic and kinetic parameters, is given. The result deviates significantly from what would be predicted if the reactions were considered to be independent.
Silicon-29 spin-lattice relaxation times and 29Si{1H} nuclear Overhauser enhancements are reported for five trialkylsilanes and fo sym-tetramethyldisiloxane, all of which contain a direct SiH bond. Relaxation rate contributions from (Si, H) dipolar interactions and fro other mechanisms are evaluated and discussed in terms of molecular mobility. For the smaller molecules it is concluded that the spin-rotation contribution to (T1)-1 is dominant but, when the alkyl groups are bigger than ethyl, dipolar interactions are more important than spin-rotation. Silicon-29 chemical shifts and coupling constants are also presented and briefly discussed.
29Si and 13C spin-lattice relaxation times and the corresponding nuclear Overhauser enhancements have been measured for PhnSiH4−n (n = 1, 2, 3), for Ph2SiHMe and for Ph2SiCl2. Thence dipolar and other contributions to the relaxation rates have been separated. The dipolar rates are used to discuss internal rotation about the phenyl-Si bond, and overall motional anisotropy. The value of T1(Si) for PhSiH3 is very short and, it is suggested, is dominated by the spin-internal-rotation interaction. Values of chemical shifts and coupling constants are also presented and briefly discussed.
The relaxation mechanism of electronically excited 8-hydroxypyrene-1,3,6-trisulfonic acid (HPT) and 6,8-dihydroxypyrene-1,3-disulfonic acid (DPD) has been studied using flash perturbation method in aqueous solution. The recombination rate constants kr of the solvated electron (ejected from the excited state of the dissociated acids) have been determined. No electron ejection takes place in aqueous 8-aminopyrene-1,3,6-trisulfonic acid (APT).
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