Multistep Laser Photoionization of the Lanthanides and Actinides

Abstract

Multistep laser photoionization has been applied to determine a number of important physical properties of heavy atoms with complex spectra including ionization potentials,(1,2,3,4,5,) energy levels,(4,6) lifetimes of levels,(1,2,4,6,7) branching ratios,(7,8) oscillator strengths,(2,5,7,8) isotope shifts,(9,10,11) hyperfine structure(9,12,13) and autoionization.(2,3,4,5,14) Ionization potentials are useful in the description of systematic trends of the elements and in understanding chemical bonding in gaseous molecules. They are used in the calculation of ion densities in high temperature metal vapors and gaseous mixtures of known temperature. Oscillator strengths are employed for obtaining concentrations of elements in high temperature media and plasmas that emit the spectral lines of the elements. The latter two uses are frequently made by astronomers.Energy levels are used in determining the electronic structure of atoms. For most of the lanthanides and actinides, this has been accomplished by conventional spectroscopy. However, additional levels in the neutral atoms of these elements are easily found by laser techniques, especially at high excitation energy or near the ionization limit where conventional sources usually fail because of the very low absorption intensities for these levels and their low population in emission sources.Lifetimes, oscillator strengths, branching ratios, isotope shifts, hyperfine structure and autoionization structure are all critical parameters in atomic vapor laser isotope separation, (2,6,10,15,16,17) while the first three are important in potential laser excited atomic vapor processes. Isotope shifts and hyperfine structure are useful in determining energy levels, in assigning these energy levels to the different electronic configurations of an element and in determining nuclear properties of isotopes of the elements, but we will not discuss these applications here. We should mention that 0-8412-0568-X/80/47-131-381$11.25/0

Ionization spectra of neodymium and samarium by resonance ionization mass spectrometry

“…Although RIS is normally used to detect atoms either by the electron or the ion generated in the photoionization process, the detection of either of these species can also be used to study the absorption spectra of amenable atoms. Worden et al (3) have used a several-color resonant photoionization process to identify upper Rydberg states and determine ionization potentials of lanthanides and actinides. Their study made use of an atomic beam; one or two lasers were tuned to generate a particular excited state, and with a tunable laser, the autoionizing and ionizing energies of the species could be identified.…”