E. F. Worden, R. W. Solarz, J. A. Paisner, and J. G. Conway, "First ionization potentials of lanthanides by laser spectroscopy*," J. Opt. Soc. Am. 68, 52-61 (1978)

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
$5.464\left(\begin{array}{l}+12\hfill \\ -2\hfill \end{array}\right)$ was obtained. When plotted against N, the lanthanide ionization limits normalized to correspond to ionization from the lowest level of f^{N}s^{2} to the lowest level of f^{N}s form two straight lines connected at the half-filled shell.

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Two-step photoionization threshold results. The numbers in parentheses following values in the table are the uncertainty in the last digit of that value.

Excitation wavelengths (λ_{1}) and excited level values are from Ref. 15 and references therein.
Uncertainties are generally larger than the precision of individual threshold determinations. They are set so that application of the uncertainty results in overlap of the values.
8065.479 cm^{−1}/eV was used to convert the values from cm^{−1} to eV.

TABLE II

Three-step photoionization threshold results. The numbers in parentheses in the table are the uncertainty in the last place of the value it follows.

Excitation wavelengths (λ_{1} and λ_{2}) and excited level values are from Ref. 15 and references therein except for Ce and Ho which were determined by laser techniques, Ref. 12.
Uncertainties are generally larger than the precision of individual threshold determinations. They are set so that application of the uncertainty results in overlap of the values.
8065.479 cm^{−1}/eV was used to convert the cm^{−1} values to eV.

TABLE III

Some lanthanide Rydberg series limits determined by stepwise laser spectroscopy techniques. The numbers in parentheses in the table indicate the uncertainty in the last digit of the value.

Excitation wavelengths (λ_{1} and λ_{2}) and excited level values given to 0.01 are from Ref. 15 and references therein.
No value of λ_{2} is given for two step observations when λ_{2} is scanned. Values given are λ_{2} for three step results.
Level values are from the following references: Nd, Ref. 17; Sm, Ref. 18; Eu, Ref. 19; Dy, Ref. 20; Ho, Ref. 21; and Er, Ref. 22.
8065.479 cm^{−1}/eV used to convert values for cm^{−1} to eV.
This excited level wavelength and energy were determined by laser techniques, Ref. 12.

Reference 14. This reference also contains a collection of limits determined by other techniques up until 1975.
Reference 1. This reference is a collection of the best available limits derived by spectroscopic techniques up to the date of publication in 1974. The Tm and Yb Rydberg convergence values are given in the last column and are replaced here by values of Reader and Sugar from Ref. 13.
Interpolated value from equation in Fig. 11 (see text).
Reference 3.
Reference 4 and 5.

Tables (4)

TABLE I

Two-step photoionization threshold results. The numbers in parentheses following values in the table are the uncertainty in the last digit of that value.

Excitation wavelengths (λ_{1}) and excited level values are from Ref. 15 and references therein.
Uncertainties are generally larger than the precision of individual threshold determinations. They are set so that application of the uncertainty results in overlap of the values.
8065.479 cm^{−1}/eV was used to convert the values from cm^{−1} to eV.

TABLE II

Three-step photoionization threshold results. The numbers in parentheses in the table are the uncertainty in the last place of the value it follows.

Excitation wavelengths (λ_{1} and λ_{2}) and excited level values are from Ref. 15 and references therein except for Ce and Ho which were determined by laser techniques, Ref. 12.
Uncertainties are generally larger than the precision of individual threshold determinations. They are set so that application of the uncertainty results in overlap of the values.
8065.479 cm^{−1}/eV was used to convert the cm^{−1} values to eV.

TABLE III

Some lanthanide Rydberg series limits determined by stepwise laser spectroscopy techniques. The numbers in parentheses in the table indicate the uncertainty in the last digit of the value.

Excitation wavelengths (λ_{1} and λ_{2}) and excited level values given to 0.01 are from Ref. 15 and references therein.
No value of λ_{2} is given for two step observations when λ_{2} is scanned. Values given are λ_{2} for three step results.
Level values are from the following references: Nd, Ref. 17; Sm, Ref. 18; Eu, Ref. 19; Dy, Ref. 20; Ho, Ref. 21; and Er, Ref. 22.
8065.479 cm^{−1}/eV used to convert values for cm^{−1} to eV.
This excited level wavelength and energy were determined by laser techniques, Ref. 12.

Reference 14. This reference also contains a collection of limits determined by other techniques up until 1975.
Reference 1. This reference is a collection of the best available limits derived by spectroscopic techniques up to the date of publication in 1974. The Tm and Yb Rydberg convergence values are given in the last column and are replaced here by values of Reader and Sugar from Ref. 13.
Interpolated value from equation in Fig. 11 (see text).
Reference 3.
Reference 4 and 5.