Lanthanide actinides, multistep

We will discuss the application of multistep laser excitation and ionization to determine the physical properties mentioned above in the lanthanides and actinides with emphasis on the determination of accurate ionization potentials. The discussion will point out how the laser techniques can circumvent many of the experimental obstacles that make these measurements difficult or impossible by conventional spectroscopy. The experimental apparatus and techniques described can be employed to measure all the properties and they are typical of the apparatus and techniques employed generally in multistep laser excitation and ionization. We do not claim completeness for literature cited, especially for laser techniques not involving photoionization detection. 

Oscillator strengths or absorption cross sections may be obtained by applying saturation spectroscopy techniques to multistep photoionization spectroscopy. A few transitions in uranium have been studied.One of the advantages of saturation spectroscopy is that it can be applied to any one of the steps in the schemes shown in Fig. 2. The disadvantages are that the experimental requirements are severe (laser-atomic beam interaction area,-frequency,-band width and-polarization) and interpertation of the data can be complex. A detailed discussion will not be given because little application has been made to the lanthanides and actinides. We will discuss in the Autoionization section the determination of photoionization cross sections by a saturation method. 

The measurement of isotope shifts and hyperfine structure (hfs) is possible in multistep laser excitation and ionization if one of the excitation lasers in the excitation schemes shown in Fig. 2 is a narrow band laser and if a collimated atomic beam is used as the source of absorbing atoms. The rest of the aparatus can remain as used for other studies. The narrow band laser(s) may be a pressure tuned pulsed dye laser ( 100 MHz, 0.003 cm l) or a CW dye laser (30 MHz to 30 KHz, 10- to 10 6 cm-- -). The atomic beam should be collimated to reduce "Doppler" broading to the level required to attain the resolution needed for investigating the structure and to fully utilize the narrow band width of the laser. A band width of 10cm-- - is usually adequate for most investigations of lanthanides and actinides. A portion of the scan laser beam is directed to an etalon and detector (interferometer) to provide relative frequency calibration. 

In this review of multistep laser photoionization of the lanthanides and actinides, we hope that we have introduced the reader to a number of laser techniques for determining spectroscopic properties of these elements. We have undoubtedly overlooked some techniques and some papers on the subjects we did cover. The importance of laser methods in studying the spectroscopy of the lanthanides and actinides is well established and future applications should greatly expand our knowledge of these elements. 

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