W R S Garton

Atomic absorption spectroscopy in the 100-600 a wavelength range.

Previous obstacles to observation of line absorption spectra in the vacuum uv below 600 A have been overcome by: (a) development of a containment device for metal vapors in a windowless system and with a negligible pressure of background gas; (b) use of a compact source of background continuum; and (c) exploitation of a normal incidence grating spectrograph which can be used with (b) to a wavelength below 300 A. As examples, the inner shell absorption spectra of Ar, Kr, Xe, Na, K, and Rb are reproduced. Slight modification of the techniques under (a) and (c) can be used when an electron synchrotron background continuum is substituted for (b).

Ultra-violet extensions of the arc spectra of the alkaline earths: The absorption spectrum of strontium vapour

The absorption spectrum of strontium vapour in the quartz ultra-violet and Schumann region has been obtained at good dispersion, leading to extension of the singlet principal series to n = 33 and discovery of 94 lines due to double-electron transitions, most of which are classifiable within six series converging on the Sr II 4 2D metastable term. Pronounced autoionization resonance effects occur in the Schumann region. We reclassify as 4d6p 3D° a triplet term previously listed as 4d6p 3F°.

A demountable flash-discharge tube for production of the Lyman continuum

Constructional and operating details are given for a high-intensity flash-discharge tube, used for generating a continuous emission spectrum which serves as background for the observation of far ultra-violet absorption spectra.

On the Levels of the p2-Configuration in the Arc Spectra of Zn, Cd and Hg

The p2 3P2 level in the arc spectra of Zn, Cd and Hg has long been considered missing; the accepted explanation has been that transitions involving the level are excessively weakened by auto-ionization. By observation of the arc spectra of these elements in the range 1700-2350 A, the level in question has been located in Zn and Cd and possibly in Hg. With increasing atomic number auto-ionization increases very greatly, so that one of two diffuse lines in CdI has previously been considered a band of Cd2. Intensity measurements on this line indicate a natural-broadening profile, and yield a value for the auto-ionization probability. Previous placing of the p2 3P0 level of HgI is considered erroneous, and a new position suggested.

Rotational analysis of a new electronic transition of HBr and DBr

The authors report new observations at high resolution of the absorption spectra of HBr and DBr using synchrotron radiation as the background continuum source. The new spectra reveal overlapping rotational structure in the region 1100-1200 AA. They have been able to analyse the 1 Sigma -1 Sigma + band originating from the ( sigma 2 pi 3)6p pi configuration. Rotational constants have been determined for both HBr and DBr, and electronic configuration assignments are proposed for most of the bands between 1280 and 1100 AA.

Line-reversal measurements of excitation and electron temperature in a shock tube

The spectral line-reversal method has been applied to determine population temperatures within an (argon-calcium) plasma, generated by a reflected aerodynamic shock. The measurements have been made simultaneously on (i) normal bound-bound Ca I lines, and (ii) lines involving strongly auto-ionizing levels. The agreement of the two sets of values identifies the electron temperature with the temperature characterizing the populations of the bound excited states, giving improved confidence in the existence of local thermodynamic equilibrium in the reflected shock.

Grating spectrophotometer for the Schumann ultra-violet range

Constructional and performance details are given of a photoelectric spectrophotometer erected for the measurement of the optical transmittances of small solid specimens, in the range above 900 A. The instrument incorporates a one-metre radius, 600 lines/mm concave grating, and scanning of the spectrum across the exit slit is performed by a linear movement of the centre of the Rowland Circle. The mechanical and electrical arrangements permit rapid measurements, quick exchange of specimen and the direct reading of transmittance on a 0-100 scale.

Configuration interaction effect on diamagnetic phenomena in atoms: strong mixing and Landau regions

We present a systematic densitometer mapping of diamagnetic effects on the principal series of Ba and Sr in absorption, with magnetic fields up to 4.7 T. The n- and l-mixing spectra are resolved in both σ- and π-polarization while the quasi-Landau resonances are observed near and above the ionization limit only in σ-polarization. Configuration interaction produces striking differences in the intensities and spacings of the n- and l-mixed spectra while only the shapes of the quasi-Landau resonances depend on the atomic systems.

Interchannel interactions and series quenching in the 5d and 6s spectra of Pb I

The absorption spectrum of lead vapour in the range 320-1070 A has been obtained. More than 60 transitions have been, found, mostly arrangable in series, which are due to excitation of either a 5d or 6s electron. Pronounced inter-channel interactions occur, similar to those in the corresponding spectrum of Tl I. Our observations confirm the applicability of a ‘ spectator model ’ for 6s excitation. The comparatively low energy of the double ionization threshold results in quenching of all but one 5d excitation series.

Flash-Absorption Spectra of the Plasmas of Arcs and other Discharges

A technique is described in which a heavily loaded flash discharge is employed as a background source for observation of absorption spectra, when the absorbing gas column is strongly excited and, therefore, itself brightly luminous. Examples of the absorption spectra of the plasmas of several arc discharges, of both open and screw-stabilized type, are reproduced. Photometric determination of the total absorption under a number of lines, combined with relative emission intensities, yield values of line-reversal temperatures; some first results are reported for copper arcs.