Table of contents

Using the beam-foil technique four new identifications in Ne VIII corresponding to transitions between n = 4, 5 and n = 3 levels have been obtained in the spectral region 175-300 Å. The lifetimes of the four n = 4 levels are reported and compared with other experimental and theoretical results.

The spectrum of eleven times ionized titanium has been observed by using a condensed vacuum-spark discharge and a 5-m grazing-incidence spectrograph and a 3-m normal-incidence spectrograph. Fortythree lines have been identified in the region 52-960 Å. The ns- and np-series have been extended to n = 6 and the nd- and nf-series to n = 8. The derived ionization energy of Ti XII is 2 351 100±60 cm^-1 (291.49 eV).

Configuration with two open shells of the type msnl from the spectra of Yb I and Lu II are analysed with respect to the hyperfine interaction. Radial integrals are evaluated from relativistic self-consistent-field wave-functions. Formulas are presented for the magnetic dipole and electric quadrupole interaction constants using the effective-operator formalism on LS coupled wavefunctions. The spin polarization contributions to the magnetic dipole interaction constants in a general msnl configuration are also presented. From such configurations in Yb I and Lu II, mean values of the electric quadrupole moments have been evaluated, giving Q(¹⁷³Yb) = 3.6 b and Q(¹⁷⁵Lu) = 5.3 b (uncorrected for the Sternheimer effect).

The fine structure theory of ⁴Π states in diatomic molecules is reconsidered from the point of view of exact numerical diagonalization of the four-by-four perturbation matrix. The interaction with other electronic states is accounted for through a second order Van Vleck transformation. Centrifugal distortion corrections are also added to the matrix elements, and a new spin-spin matrix element of the type ΔΛ = -ΔΣ = ±2 is in particular found to contribute to the Λ-doubling. The theoretical results are applied to the a⁴Π_u state in O₂⁺ and the B⁴Π state in VO.

The spectrum emitted by an electrodeless discharge tube filled with pure ¹³⁰Te has been investigated by Fourier transform spectroscopy. The observations have led to a list of wavenumbers and estimated intensities for 277 lines in the range 3 678 to 11 761 cm^-1. Zeeman structures for 90 lines were studied. 70 levels, 65 of them being new, have been found and 170 lines have been classified. For these levels the energy is given with an accuracy equal to 0.005 cm^-1. Landé factors for 46 levels have been measured with an accuracy up to 0.003 U.L. Parametric studies performed on 5s²5p³-(6s+7s+5d+6d) configurations on the one hand and on 5s²5p³(6p+7p) on the other hand, give a good interpretation for most of the levels; the r.m.s. deviation of the level energy between theory and experiment is equal to roughly 30 cm^-1.

Many infrared lines permitted for second-order radiation, magnetic dipole, electric quadrupole or mixed types, have been observed in the arc spectrum of tellurium and in the spark spectrum of iodine. These lines are due to transitions between the levels of the ground configuration 5s²5p⁴. The Zeeman effect of the lines of tellurium (isotope 130) has supplied Landé factors for the [³P₂], ³P₁ and [¹D₂] levels. Furthermore, a direct observation of the "interference effect" between magnetic dipole and electric quadrupole radiations has been made on the [¹D₂] → [³P₂] transition. The hyperfine structure of tellurium (isotope 125, nuclear spin I = ½) was observed for four transitions, by means of which the interaction constants A([³P₂]), A(³P₁) and A([¹D₂]) have been determined. The hyperfine structure observed on the ³P₁ → [³P₂] line of ¹²⁷I II (nuclear spin I = 5/2) supplied the constants A([³P₂]), A(³P₁), B([³P₂]), B(³P₁). Parametric studies of these hyperfine structures suggest that relativistic and core polarization effects are predominant.

The Zeeman effect of the 6 476 Å mixed multipole (or so-called forbidden) line was studied with a Fabry-Perot interferometer and a tri-prism spectrograph in magnetic fields of 1.3, 1.5, 1.7 and 2.0 kG. The relative intensities of the ΔM = ± 1 and ΔM = 0, ± 2 transitions for longitudinal and transverse directions of observations are calculated as functions of the external magnetic field and electric-quadrupole admixture. The differences between the relative intensities of ΔM = ± 1 Zeeman patterns observed in two directions are due to the interference of the magnetic-dipole and the electric-quadrupole radiation. A comparison of the computed and experimental intensities shows that this line has predominantly a magnetic-dipole character with the percentage of the electric-quadrupole radiation in this line being about 18 ± 4.5%. This result is in good agreement with the value obtained by Garstang.

The ³Σ^- ground states of AsH and AsD have been investigated in order to study the J-dependence in the spin-orbit coupling. At least for AsD such a J-dependence is observed.

The possibility is being discussed of creating and heating the plasma in "Tornado" magnetic traps by means of the rotating plasma technique. On account of the particular field geometry of these traps, it is likely that the critical velocity phenomenon of rotating plasmas can be avoided.

At least 26 metals transform at ordinary pressure from a low temperature close-packed structure to a high temperature bcc phase. According to an old hypothesis of Zener, this is caused by a somewhat lower Debye temperature in a bcc lattice. This idea is investigated in detail and confirmed both by theoretical calculations and analysis of experimental data. Most polymorphic transformations occur quite close to the melting temperature but even so, anharmonicity does not cause the change in crystal structure.

The paper considers the role of the electronic and magnetic free energy in stabilizing the frequently observed high temperature bcc phase in metals. For transition metals, the conduction band density of states depends on the lattice structure but yet the corresponding difference in the temperature dependence of the free energy is in general not large enough to be the main reason for the polymorphism. This is discussed in some detail for titanium and zirconium. For rare earths, neither the conduction electrons nor the localized 4f states are effective in stabilizing a high temperature bcc structure. The form of the free energy well above the Curie temperature is compared for the localized and the itinerant models of magnetism. Although the band model gives a good description for most weakly magnetic systems, iron is an exception in this respect. Finally, it is concluded that a somewhat lower Debye temperature for the bcc lattice remains a major reason for the close-packed to bcc structural transformations of transition metals.