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The emission spectrum of doubly and triply ionized gadolinium from 1200 to 6000 Å is reported. A pulsed hollow-cathode light source was used with a 5-m Czerny–Turner vacuum spectrograph to obtain wavelengths and photoelectric intensities for 12 000 lines of doubly ionized gadolinium and 8000 lines of triply ionized gadolinium. For the fourth spectrum, a preliminary analysis indicates that the 4f^66s–4f^66p transitions occur at 45 000 cm^−1 and the 4f^7–4f^65d transitions at 75 000 cm^−1. The stronger lines from these regions determine 32 low-lying levels of these configurations.

The optical absorption spectra of 1% Gd:LaBr_3, 5% Gd:LaCl_3, GdCl_3, 2% Gd:Y(OH)_3 and Gd(OH)_3 at 1.5 K in high resolution are given over the region 31 000 cm^-1 to 41 000 cm^-1. Reduced matrix elements based on intermediate-coupling free-ion calculations are used to perform a crystal-field analysis for Gd^3+ in a 6¯(C_3h) symmetry electrostatic field. A least-squares fit to levels in each crystal has led to the assignment of M quantum numbers to most levels and of B_k^q parameters to each crystalline host.

The spectral of the rare earths have been photographed under controlled excitation so that either the spectra of the doubly or triply ionized elements are brought out with maximum intensity. A mild excitation is used in addition to give the first and second spectra for comparison. Some regularities are immediately apparent and vary very gradually through the rare-earth group. The general features of the spectra are discussed in this paper.

A sealed-off hollow cathode discharge tube with iron electrodes and rare gas filling is described which will give an iron spectrum with very sharp lines and intensities of high reproducibility. Extensive data are given of the dependence of the iron intensities on the character of the rare gas, its pressure, and the discharge current. For most purposes a neon filling at about 3 mm pressure is recommended. The lines of such a tube are recommended for wavelength standards. They may serve as intensity standards with the proper precautions.

Further studies of the spectral data obtained in the February 1960 rocket experiment [ Ann. Geophys.17, 109 ( 1961)] have confirmed much of the preliminary analysis. New bands of the Lyman–Birge–Hopfield system in the 1700–2200 Å region have been identified. More precise wavelength determinations have been made, and previously indicated bands of N_2 have been more positively identified. The Lyman α line of hydrogen is just detectable. The intensity distribution among the various bands during weak auroral conditions is shown to differ markedly from more intense displays. Laboratory data obtained from a microwave discharge in very pure N_2 show good correlation with some features of the rocket spectra.

A new type of slit mechanism is described which operates on the principle of the proving ring or loading ring. The load applied to distort a steel ring is the means by which the slit openings are varied and the opening determined. Very simple devices are described in which straight slit jaws are connected to opposite sides of a flexible ring and known weights are applied to the ring to obtain the desired slit opening. The mechanism has been used to provide very long dual curved slits for Ebert type monochromators, in which the proving ring itself acts as one jaw of the curved slits. The dual slits have been actuated by hydraulic pressure for vacuum operation.

With the help of an automatic electronic switch placed between phototube and recorder of a spectrograph, the intensities as function of time of a series of spectrum lines produced in a spark have been recorded. The changes as function of the position in the gap were also investigated. There is an extensive afterglow which in general decays faster for the higher stages of ionization. The continuous background has the same characteristics as the spectrum of the surrounding gas. The changes in self-absorption excitation and line profile were also studied as function of time and partly correlated with the fundamental processes responsible for the afterglow.

Groups of iron lines with relative intensities independent of excitation are proposed to serve as intensity standards for rapid and reliable plate calibration. One such group between 3140 and 3240A has been tested under a great variety of conditions and found to be satisfactory for this purpose. Lines of Fe I selected at random in general have their relative intensities changed much more by self-reversal than by changes in excitation. A general quantitative study of self-reversal was made which allows an estimate of the degree of self-reversal of any line under given conditions. Weak or moderately strong lines coming down to all but the lowest levels are free from self-reversal under the conditions at which arcs or sparks are usually operated.

An electronic device is described which renders a phototube sensitive only at prescribed but arbitrary intervals of a spark cycle. Such undesirable light, as air lines and continuous background, can then be suppressed. There is evidence that for spectrochemical analysis purposes the spectrum thus recorded photoelectrically combines the stability and reproducibility of the condensed spark with the sensitivity of the dc arc.

An arrangement is described by which spectroscopic wavelength measurements are greatly simplified with an increase in accuracy. The measuring microscope is replaced by a photoelectric scanning device which displays line contours on an oscilloscope screen. The comparator readings are made automatically with electronic devices, and the results either recorded with an automatic typewriter or punched into cards or both. Photographic densities are measured and recorded at the same time. The data are then further processed by electronic calculating machines.The equipment is built largely from commercially available components. Its operation is simple and foolproof. The various stages are independent of each other and can be introduced singly or in combination as desired.

The absorption spectrum of YbCl_3·6H_2O has two sharp lines near 9700 A which are interpreted as the transitions from the M=5/2 Stark component of the ^2F_7/2 level of the Yb^+++ ion to the M=3/2 and 5/2 levels of the other doublet component ^2F_5/2. The Zeeman splittings of the two lines were investigated at 4°K as a function of the orientation of the crystal. They can be interpreted by assuming that the crystal field has a pronounced magnetic symmetry axis (probably sixfold) perpendicular to the twofold symmetry axis of the crystal. The magnetic ellipsoid is degenerate into a pair of planes perpendicular to this axis. The direction of the magnetic axis is slightly different for the three observed states and bears no relation to the optic axes of the crystal.

A new scanning spectrometer is described herein which is based almost exclusively on very recent technological advances and which, over the ultraviolet, visible, and near infrared region to 6 microns is capable of resolution and wavelength measuring accuracy comparable, on a wave-number basis, with the best that has been accomplished with spectrographs limited to the photographic region. The instrument is of the Ebert type and employs gratings as large as 5×7 inches, has a focal length of 72 inches, uses circularly curved slits 2 inches long, and can be triple passed. Specifications and performance are outlined.

The present status of our knowledge of the structure of the spectra of the doubly and triply ionized spectra of the rare earths is derived partly from experimental data of the emission spectra of the free ions which provide the energy level scheme in great detail but are difficult and laborious to analyze. For the lower levels knowledge of the structure comes from the crystal absorption and fluoresence spectra. In all cases approximate theoretical calculations of the energies are essential.