M. W. D. Mansfield

Observation of an 'Atomic Plasmon' Resonance in the Ba I Absorption Spectrum between 10 and 200 angstrom

The observation of a broad ‘atomic plasmon’ resonance, recently predicted by Wendin is reported, together with a number of discrete features due to excitation of a single electron from the 4d subshell in Ba I. HartreeFock calculations indicate mixing between configurations built on 4d9 5p6 6s2, 4d9 5p6 5d 6s and 4d9 5p6 5d2 of Ba II. Discrepancies between Wendin’s theory and experiment are attributed to this mixing. The spectrum near 16 Å arising by excitation of the 3d subshell has also been observed.

Observation of a 'giant resonance' in the 3p absorption spectrum of Mn i

The absorption spectrum of Mn I in the energy region corresponding to excitation of the 3p-subshell (40-70 eV) has been recorded for the first time. At least 10 discrete features are reported, as well as a broad modulation in the continuous absorption immediately above the 3p-thresholds. The spectrum is discussed in relation to previous photoabsorption data for nearby elements in the periodic table, and assignments are made by comparison with Hartree -Fock model calculations. The spectrum is dominated by a 3p-3d ‘giant resonance’.

On the simultaneous excitation of two electrons in neutral atomic zinc

In a new investigation of the Zn i absorption spectrum between 400 and 1000 Å, 11 series due to the simultaneous excitation of two electrons have been observed for the first time in Zn i. At least 120 double excitations have been measured. They are identified by comparison with published Zn ii energy levels and with Hartree-Fock calculations. The new lines may be divided broadly into two groups, a longer wavelength group (900-990 Å) due to simultaneous excitation of the two valence electrons, and a shorter wavelength group (420-610 Å) due to simultaneous excitation of one valence and one sub valence subshell electron. A detailed examination of the two groups of two-electron transitions indicates that, in both cases, excitation occurs by a final state configuration mixing process related to conjugate shake-up.

Centrifugal Barrier Perturbation of the

Hartree-Fock calculations for the nf 2F0 series of Ba II are reported. Several of the nf wavefunctions are found to be shared between the inner and the outer wells of the double valley potential. The resulting anomalies in intensity, spin-orbit splitting and quantum defect provide a qualitative explanation for some recent observations.

n

New Pb I absorption spectra show discrete structure due to excitation of the 4f subshell and continuous absorption beyond the 4f thresholds. The results are compared with those previously obtained in Tl I and Hg I, and the presence of additional maxima in the Pb I spectrum is accounted for by comparison with recent independent-particle non-relativistic central field calculations.

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In the light of recent work on shape resonances in diatomic systems, the question of a possible persistence of atomic centrifugal barrier effects in molecules arises, particularly as regards resonant penetration of f-waves. Experiments on selenium vapour suggest that two cases may be expected depending on whether localized f states are present or not in the atom. The evidence in Se is that f waves mainly external to the atom are scattered into several channels by the anisotropic molecular field and that damping of the f-maximum results. A reason is suggested for which inner shell absorption spectra of solids may not faithfully reproduce the density of states of the conduction band, even for elemental materials.

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New observations of the absorption spectrum of neutral Tl, in the wavelength range 320‒1300 Ň are reported. Earlier observations and an analysis by Connerade (1972) are confirmed and extended. Present observations include 142 new transitions, mostly outside the previous energy range, which have been classified, mainly within the scheme proposed by Connerade (1972). The absence of some series due to excitation of one electron from the 5d subshell is noted and is attributed to the occurrence of strong series due to simultaneous excitation of two electrons.

F Series in BaII

New structure in the absorption spectrum of Zn I vapour between 70 and 105 Å is reported. The experiment was performed by using the continuous radiation of the Bonn 2.5 GeV synchrotron as background source. The structure is due to excitation of the 3s2 subshell. A comparison with semi-empirical and Hartree-Fock predictions is made.

Potential Barrier Effects Beyond the 4f Photoionization Thresholds in Pb I

A modification of the vapour containment technique has enabled the X-u. v. absorption spectrum of Rb I vapour to be recorded at higher vapour densities than previously attainable. Twenty seven new transitions have been detected. These include a group of resonances extending up to 5eV above the 3d thresholds and absorption lines attributed to excitation of the 3p subshell. The analysis of Mansfield & Connerade (1975a) is extended in the light of the new data and of further comparisons with Hartree-Fock calculations.

Molecular Damping of Centrifugal Barrier Effects in the 3d Absorption Spectrum of Selenium Vapour

The absorption spectrum of Eu I between 40 and 300 Å has been recorded. Prominent structure due to the excitation of the 4d subshell has been found. The spectrum closely resembles that reported for Eu metal (Zimkina, Fomichev, Gribovskii & Zhukova 1967), although many additional resonances are resolved in the present work. It is dominated by a ‘giant resonance’, attributed to 4d→(4f, εf) transitions, and occurring above the main threshold for 4d ionization. Identifications of the main features are proposed and are supported by Hartree–Fock calculations. Evidence of a 4d→np series has also been found.