Dipolar Parameters Research Articles

Laser-Stark spectrum of methyl alcohol at 890.761 GHz with the HCN laser

The laser-Stark spectrum of methanol has been studied up to Stark fields of about 55 kV/cm with the 890.761-GHz HCN laser, in both parallel and perpendicular polarizations. Extensive series of absorption lines have been assigned to the J = 6 to 15 members of the k = 6 ← 5 Q branch of the v = 0 E torsional state of CH 3OH. Also, 21 M components of the J k = 7 1 ← 6 2 A ± doublet in the v = 1 excited torsional state have been identified. Efforts to analyze the Q-branch spectra in terms of dipolar parameters and zero-field frequencies were hampered by very high statistical correlations in the least-squares fits. However, it proved necessary to permit the upper-state value of μ a to exceed that of the lower state, by 0.0014 D, and to introduce J dependence of μ a . Analysis of the Stark shifts of the excited torsional state transition yielded a μ a of 0.93 D, about 0.04 D greater than the mean value for the ground state.

Simulation of field-induced thermally stimulated currents in dielectrics. Application to the dipolar case in polymeric systems

Numerical calculations of thermally stimulated depolarization currents (TSDC) and thermally stimulated polarization currents (TSPC) have been carried out by using the bistable model of Fröhlich and taking into account the temperature dependence of equilibrium polarization according to a Langevin function. For dipolar processes characterized by a single relaxation time as well as by a spectrum of relaxation times obeying classical distribution functions (Wagner, Cole-Cole, Fuoss-Kirkwood, Davidson-Cole, Havriliak-Negami), the following predictions have been obtained: (1) A TSDC peak must be always of larger magnitude than the corresponding TSPC peak as a result of an increase in polarization taking place during the cooling step; (2) For the same reason, the magnitude and area of a TSDC peak must be dependent on the cooling rate adopted in the poling process; it also follows that, unless an instantaneous cooling is postulated, such a peak can no more be considered as depicting the relaxation properties of the material at the temperature of polarization; (3) A TSPC peak must be followed by a significant current reversal as a necessary result of the tangential convergence of the transient polarization with its decreasing saturation limit in the high-temperature range. These predictions have been tested in a polymeric system selected for its well resolved relaxation spectrum (styrene-butadiene block copolymer). Full qualitative agreement between experiment and theory has been found as far as the behavior of the α relaxation (glass transition) is concerned. These results show that the variations of equilibrium polarization occuring during the nonisothermal steps of TSDC and TSPC experiments cannot be a priori neglected, as is still commonly done for the determination of dipolar relaxation parameters.

Molecular pair effects and the breakdown of Onsager’s dielectric theory

The source of breakdown of Onsager’s dielectric constant formula for simple polar fluids of high dielectric constant is identified as a purely electrostatic two cavity effect. An estimate of this effect yields a Kirkwood g factor of the order of the dipolar strength parameter 4π/3 ρu2β.

The1H N.M.R. spectrum of cyclopentadiene dissolved in a nematic liquid crystal

A 220 MHz 1H spectrum cyclopentadiene monomer dissolved in a nematic phase has been obtained and analysed to yield a set of dipolar coupling constants and orientation parameters. Ratios of interproton distances have been calculated from the dipolar couplings, taking into account averaging over harmonic vibrations.

Extended Frenkel excitons in one-dimensional narrow-band systems

A model is developed for excitons in a linear chain of dimers of radical ions in the region intermediate between the nearly free-electron limit and the localized-electron limit. When only on site electron—hole interactions are taken into account, an extended exciton state results, which in the limit of zero bandwidth is the normal Frenkel exciton solution. For the case of RbTCNQ, it is shown that from a comparison of the experimentally found dipolar splitting parameters and the calculated ones, it may be concluded that the on site electron—hole interaction and the one-electron bandwidth are of the same order of magnitude for this salt.

Critical Behavior of Magnets with Dipolar Interactions. III. Antiferromagnets

Exact renormalization group recursion formulas, derived in Paper I for $\ensuremath{\epsilon}=4\ensuremath{-}d$ small, are applied to antiferromagnets. It is shown, that in contrast to the ferromagnetic case, the main parameters characterizing the dipolar interactions become irrelevant for antiferromagnets, so that the critical exponents maintain their short-range values. However, the relative decay of the dipolar parameters is slow (the appropriate exponents being of order ${\ensuremath{\epsilon}}^{2}$), and thus the possibility of observing their existence experimentally is discussed briefly. In addition, the dipolar anisotropies, deriving from the lattice structure, produce weak instabilities which are even harder to detect than in the ferromagnetic case. Ferromagnetic short-range anisotropy is considered briefly. The Appendix contains a calculation of the renormalization group eigenvalues of the operators $\ensuremath{\Sigma}{S}_{\stackrel{\ensuremath{\rightarrow}}{\mathrm{R}}}^{4}$ and $\ensuremath{\Sigma}{({S}_{\stackrel{\ensuremath{\rightarrow}}{\mathrm{R}}}^{a})}^{4}$. The latter is shown to be relevant.

The mechanism of the low-temperature dielectric relaxation of polymers containing low molecular weight impurities

The temperature-frequency functions for the dielectric losses and dielectric constants of low molecular weight substances (methyl methacrylate, anisol) present in a polymer matrix (polystyrene, polymethylmethacrylate, polyphenylsilsesquioxane) have been investigated. A small molecule was found to be a kinetically independent unit of molecular movement. The fact that the dipolar polarization parameters of low molecular weight compounds presence in the polymer matrix were identical with some of the processes in polymers containing low molecular weight impurities resulted in the conclusion that the dipolar polarization mechanisms are the same in both cases.

A consistent approach of heterogeneous theory leading to a dipolar formulation—II. Calculation of heterogeneous parameters

In part I of this paper, we proposed a consistent formulation for heterogeneous theory. In part II, we give the detailed calculation of the polar and dipolar parameters used in this new formulation. We shall assume, for the sake of simplicity, that the channel contains only two concentric media: a central fuel rod and an annular cavity. We shall also assume collisions to be isotropic.