Earl F. Worden

First ionization potentials of lanthanides by laser spectroscopy

Photoionization and Rydberg spectra of ten lanthanides have been studied using stepwise laser excitation and ionization methods. These spectra were obtained from several different laser populated excited states in each case. Accurate ionization limits were derived from observed photoionization thresholds. Except for praseodymium, the observation of one or more long Rydberg progressions allowed more accurate limits to be determined. The Rydberg convergence values in eV are: Ce, 5.5387(4); Nd, 5.5250(6); Sm, 5.6437(6); Eu, 5.6704(3); Gd, 6.1502(6); Tb, 5.8639(6); Dy, 5.9390(6); Ho, 6.0216(6), and Er 6.1077(10). For praseodymium a threshold value of 5.464(+12-2) was obtained. When plotted against N, the lanthanide ionization limits normalized to correspond to ionization from the lowest level of fNs2 to the lowest level of fNs form two straight lines connected at the half-filled shell.

Radiative lifetimes, absorption cross sections, and the observation of new high-lying odd levels of 238 U using multistep laser photoionization*

We report the observation of over 100 new high-lying odd levels in atomic uranium between 32 600 and 34 200 cm−1 using tunable laser techniques. These augment the 32 odd levels previously determined in this energy regime by conventional atomic spectroscopy. The method used in these studies, multistep photoionization under pulsed dye laser excitation, was also employed to make J assignments, measure radiative lifetimes, and to obtain absorption cross sections of transitions involving these levels.

Preliminary Level Analysis of the First and Second Spectra of Dysprosium, Dy i and Dy ii*

Accurate wavelengths and wavenumbers of over 22 000 dysprosium lines have been measured in the wavelength region 2300–11 400 A. The Zeeman effect has been observed at a field strength of 24 000 G from 2300 to 9000 A. By comparison of relative intensities of the lines from sources under various conditions, 85% of the lines have been assigned as Dy i or Dy ii spectrum lines. From the energy-level analysis, 141 even and 197 odd levels of Dy i are known. Combinations between these levels account for 1952 lines. For Dy ii, 14 even and 214 odd levels are known, with 1000 lines classified. The ground levels of Dy i and Dy ii are 4f106s25I8 and 4f106s⁶I812, respectively. The lowest level of the 4f95d6s2 configuration of Dy i lies 7565.62 cm−1 above the ground level. The g values for most of the levels of both spectra are given.

Use of Electrodeless Discharge Lamps in the Analysis of Atomic Spectra

The application of electrodeless discharge lamps in obtaining the information necessary for the analysis of the first and second spectra of lanthanide and actinide elements is discussed. It is shown how differentiation of neutral atom and first ion lines, self-reversal, and Zeeman-effect observations may be procured using these lamps as the sole source. The procedures are illustrated by studies on Cm, Gd, and Dy.

Generalized Parametric Study of 5fN and 5fN7s Configurations

The parametric studies of 5fN and 5fN7s configurations by application of both Slater-Condon theory and the generalized least-squares method to the whole sequence of actinides has led to the simultaneous interpretation of 72 levels in first spectra (5fN7s2) and of 112 levels in second spectra (5fN7s). The determination of the N-dependence of various electrostatic parameters of the 5fN core improves the reliability for prediction of missing configurations. Revised interpretations and new energy levels are reported in a number of spectra.

Determination of absolute atomic transition probabilities using time resolved optical pumping

Abstract We describe a method of determining atomic transition probabilities by independently measuring branching ratios and radiative lifetimes. These quantities are directly determined by time resolved optical pumping. The technique has been applied to the measurement of gA values for particular transitions in 238U I.

Energy levels of the first spectrum of curium, Cm i*

The curium spectrum emitted by electrodeless lamps was observed from 2400 to 11 500 A and the wavelengths of over 13 250 lines were accurately measured. Zeeman effect and spectrum-assignment plates were photographed from 2400 to 9000 A. From data obtained on the spectrum-assignment plates, over 6800 lines were assigned to Cm i and over 4050 lines were assigned to the Cm ii spectrum. The analysis of the Cm i spectrum has produced 335 odd levels and 348 even levels that combine to classify over 5025 Cm lines. Only the energy levels are presented here. The Lande g values of most levels have been obtained from the Zeeman effect data and isotope shifts were determined for many levels. These data were useful in the assignment of levels to electronic configurations of Cm i. The ground configuration of Cm i is [Rn]5f7 6d 7s2 and the lowest level of the [Rn]5f87s2 configuration is only 1214 cm−1 above the ground level.

The ionization potential of neutral iron, Fe i, by multistep laser spectroscopy

Three-step laser excitation was used to populate and observe members of Rydberg series in neutral iron with high effective quantum numbers. These series converge to the ground and to the first excited state of singly ionized iron. The photoionization threshold was also observed. Analyses of the Rydberg series yield the value 63 737(1) cm−1 or 7.9024(1) eV as the ionization potential of neutral iron.

Laser spectroscopy of neptunium; first ionization potential, lifetimes and new high-lying energy levels of Np i

The first ionization potential of neptunium has been determined from the photoionization threshold and from Rydberg series observed by laser spectroscopy techniques. The Rydberg series convergence limits yield the most accurate value of 50 536(4) cm−1 [6.2657(5) eV]. The radiative lifetimes of five levels in the 26 200–29 050-cm−1 range have been measured. New energy levels, 27 odd and 37 even, in the 33 000–37 000-cm−1 range have been determined with approximately ± 0.5-cm−1 precision.

Ionization potential of neutral atomic plutonium determined by laser spectroscopy

The ionization potential of the neutral plutonium atom, Pu i, has been determined by two- and three-step resonance photoionization observation of the threshold of ionization and of Rydberg series. The Rydberg series were observed by field ionization as series that converge to the first ionization limit and as autoionizing series that converge to the second and to several higher convergence limits. The threshold and Rydberg series were obtained through a number of two- and three-step pathways. The photoionization threshold value for the 239Pu i ionization potential is 48582(30) cm−1, and the more accurate value from the Rydberg series is 48604(1) cm−1 or 6.0262(1) eV.