Physica最新文献

The configurations 4f¹¹6p in Ho II and Er III and 4f¹¹6p6s² in Er I have been located. Energy-level calculations of these configurations which produce the same terms are compared with experimental data.

The experimental results on the NMR investigation of the six isomorphous crystals with the K₂CuCl₄.2H₂O structure, as reported in previous papers, are analysed. The covalency effects within the CuCl₄.2H₂O^2- octahedron are described by a molecular orbital model. Good agreement between the copper electronic g tensor and nuclear hyperfine interaction tensor on the one hand, and the ligand spin-transfer coefficients on the other hand is obtained. The importance of spin transfer from the ligands towards the empty copper 4s and 4p orbitals is outlined.

The superexchange interactions in these compounds are discussed qualitatively on the basis of the ligand spin-transfer coefficients.

Sodium vapour is excited by D₂ radiation. The linear polarization of the fluorescent D₂ radiation emitted at right angles to the incident-light beam is measured as a function of the pressure of an added noble gas. A magnetic field of 270 Oe which points parallel to the incident-light beam, serves to decouple the nuclear spin in the excited state. From the decrease of the polarization observed at rising pressure, cross sections for the disalignment of the electron in the excited state are derived. They are 167, 174, 308, 341, 376 Ų for the noble gases He, Ne, Ar, Kr, Xe at 383 K. These and earlier results on sodium depolarization are summarized and compared with theoretical results by Masnou et al., Reid, and Lewis et al. Satisfactory agreement is obtained.

Experiments on an electric dipole centre, exhibiting multiple relaxation, in the natural mineral sodalite, are described. The concentration of the dipole centres is reduced upon X irradiation, whereas simultaneously colour centres and paramagnetic centres arise. Thermal bleaching restores the original concentrations. The interrelationships between these centres are established.

A model is proposed in which the dipole centre is ascribed to an interstitial monovalent metal ion (say a Na⁺ ion) acting as a charge compensator for an Al³⁺ ion, substituted for a Si⁴⁺ ion. This Al-Na complex may be destroyed by X rays, yielding an electron trapped at the sodium ion and a hole trapped at a nonbridging oxygen ion, adjacent to the Al³⁺ ion, to which both the optical and paramagnetic properties of the X ray induced centres are attributed.

The levels of the lowest term, ⁵D, in the 3d⁶ configuration and the levels of the 3d⁵ (⁶S) 4p ⁵P⁰ in the spectra of Co IV, Ni V and Cu VI have been established. A comparison is made between the intervals in these multiplets in the isoelectronic sequence Cr I-Cu VI. Predictions are given for the analogous intervals in Zn VII and the wavelength region of the corresponding lines in that spectrum.

The relationship to the IPTS-68 of the cryogenic temperature scale that has been used by Michels and collaborators at the Van der Waals-Laboratory of the University of Amsterdam is properly established.

A new theory of propagation and scattering of light in fluids is formulated. The analysis is based on a resummation of the Kirkwood-Yvon series expansion for the dielectric constant. The resummation is equivalent to a renormalization procedure recently proposed by Bedeaux and Mazur in which vacuum propagators are replaced by propagators corresponding to a continuum with dielectric constant given by the Lorentz-Lorenz formula. It is shown that the phenomenological Einstein formula for the differential scattering cross section follows naturally from the theory.

A manifestly gauge-invariant hamiltonian formulation of classical electrodynamics is constructed by taking the electromagnetic fields as the basic dynamical quantities, obeying appropriate Lie-bracket relations. The longitudinal parts of the fields can be eliminated completely from the beginning. The theory is relativistically covariant: the generators of the Poincaré Lie algebra are given explicitly. Explicit realizations of the Lie-bracket operation are derived (they are different from the usual Poisson brackets), and the relativistic Liouville equations are presented.

The classical one-dimensional gas of hard rods with an interaction of finite range is investigated. The Gibbs potential, the distribution function of a finite number of successive particles, and the average length per particle of that system are shown to be expressed in terms of the eigenvalue with the smallest absolute value and the corresponding eigenfunction of a homogeneous linear integral equation. Byckling's equation is criticized.