A spectral study of promethium and samarium in the wavelength ranges of 530 to 560 and 580 to 615 nm has been made by resonance ionization mass spectrometry. A total of 54 promethium and 35 samarium ionization wavelengths were found. These optical routes are thought to involve a single-color, three-photon process. On the basis of this premise, new qualitative spectral information for both these elements is obtained from these data, and directions for more definitive studies result.
J. P. Young, R. W. Shaw, and D. H. Smith, "Spectral Study of Promethium and Samarium by Resonance Ionization Mass Spectrometry," Appl. Spectrosc. 43, 1164-1168 (1989)