Symposia of The Faraday Society 

About: Symposia of The Faraday Society is an academic journal. The journal publishes majorly in the area(s): Liquid crystal & Magnetic circular dichroism. Over the lifetime, 61 publications have been published receiving 1307 citations.

Extended Debye theory for dielectric relaxations in nematic liquid crystals

Abstract: A theory of orientation polarization in nematic liquid crystals is developed for a molecular dipole moment parallel to the long axis of the molecule. The theory is essentially an extension of the Debye model for normal polar liquids to take into account the strong intermolecular potential which is responsible for the nematic state. It is shown in detail that the relaxation time depends strongly on the nematic potential and also on whether the polarization takes place parallel or perpendicular to the symmetry axis of the crystal. In the first case, the relaxation time increases from its value in the isotropic liquid phase by a “retardation factor” which may amount to several orders of magnitude, depending on the strength of the nematic potential. In the second case, the relaxation time decreases slightly. The calculated retardation factor is smaller than the experimental one. It is suggested that this discrepancy is due to the neglect of molecular short-range order.

A molecular field treatment of liquid crystalline mixtures

Abstract: The Maier-Saupe theory of the nematic mesophase is extended to multicomponent systems containing axially symmetric molecules interacting with a general anisotropic intermolecular potential. Expressions are derived for the anisotropic pseudo-potential of each component as well as the orientational molar Helmholtz function for the mixture. Simplified forms of these formulae are then employed, with some success, to predict the phase diagrams for two binary mixtures of nematogens. The possible application of the theory to interpret the solute activity coefficients determined by gas-liquid chromatography using a nematogen as the stationary phase is indicated.

Specular reflection spectroscopy of electrode surface films

Abstract: The optical properties of a series of nonmetallic and metallic surface films of ca monolayer thickness, which are adsorbed on metal electrodes, have been investigated by means of in situ differential specular reflection spectroscopy over the photon energy range 1.5–5.5 eV. Adsorbed O and oxide layers on Pt, Au and Ni substrates exhibit intense charge-transfer absorption bands (α≃ 105–106 cm–1). The adsorbed H-atom layer on Pt produces an “inverse electroreflectance effect”. The effects of adsorption of monolayer Ag atom films on the oxidation of Pt electrodes were studied optically. The optical properties of very thin Ag films on Pt differ markedly from those of bulk silver and very rapidly with increasing film thickness.

Polarizability and hyperpolarizability of the helium atom

Abstract: The zeroth, first and second order perturbed Schrodinger equations for the helium atom in an external electric field have been solved to high accuracy through the variation principle. A ground-state energy, differing by only about 1 part in 109 from Pekeris's extrapolated figure, was obtained with a wave function ϕ0 containing 181 adjustable parameters (compared to Pekeris's 1078). The first-order wave function ϕ1, and hence the second-order energy and polarizability of the atom, was obtained with up to 84 adjustable parameters in ϕ1. The polarizability α is 1.38319 a.u. = 0.204956 × 10–24 cm3= 0.228044 × 10–40 C2m2 J–1. The dipole shielding factor differs from its exact value of unity by a few parts in 105. The second-order wave function ϕ2, and hence the fourth-order energy and hyperpolarizability γ, were obtained for various wave functions ϕ0 and ϕ1, and with up to 106 adjustable parameters in ϕ2. Smooth convergence was obtained, yielding γ= 43.10 a.u. = 2.171 × 10–38 e.s.u. = 2.688 × 10–63 C4m4J–3. However, an extension to ϕ1 may be needed before an accurate value of γ can be computed. Accurate values have also been obtained for the δ-values of the unperturbed atom and for the quadrupole and octopole polarizabilities.

Measurement and interpretation of magnetic circular dichroism and magnetic linear dichroism spectra

Abstract: This paper deals with three problems of a different nature. We first discuss the conditions required to obtain reliable and usable magneto-optical and absorption data at any temperature down to that of liquid helium; this discussion includes the description of our cryostat and absorption device, as well as a critical study of the optimization of the signal-to-noise ratio of the instruments. Secondly, a new fitting procedure is proposed for the analysis of absorption and magnetic circular dichroism curves and the extraction of useful parameters. Finally, the significance of these parameters is examined for anisotropic centres isolated in an isotropic matrix; the results thus obtained are illustrated by means of magneto-optical experiments on CaF2+Nd3+ crystals.