Spectral Relations Between Certain Iso-Electronic Systems and Sequences. Part I; Ca I, Sc II, Ti III, V IV and Cr V

H. E. White

doi:10.1103/PhysRev.33.538

Abstract

The spectra of trebly ionized vanadium, V IV, and quadruply ionized chromium, Cr V.—The neutral atoms of vanadium and chromium contain five valence electrons, $3 d^{3} 4 s^{2}$ , and six valence electrons, $3 d^{5} 4 s$ , respectively. The removal of three electrons, $3 d 4 s^{2}$ , from vanadium and four electrons, $3 d^{3} 4 s$ , from chromium yields two iso-electronic systems, V IV and Cr V, the lowest energy levels of which arise from the two remaining electrons, $3 d^{2}$ . The spectra from these two systems should resemble very closely the spectra of neutral calcium, singly ionized scandium, and doubly ionized titanium. Extrapolations from the already known data of Ca I, Sc II, and Ti III, to V IV and Cr V have led to the identification of some thirty energy levels in both triply ionized vanadium and quadruply ionized chromium. The strongest lines in these spectra arise from combinations between ${}^{3}P$ , ${}^{3}D^{'}$ , ${}^{3}F$ , ${}^{1}P$ , ${}^{1}D^{'}$ , ${}^{1}F (3 d 4 p)$ and ${}^{3}D$ , ${}^{1}D (3 d 4 s)$ , and ${}^{1}S$ , ${}^{3}P^{'}$ , ${}^{1}D$ , ${}^{3}F^{'}$ , ${}^{1}G (3 d^{2})$ .

The irregular doublet law and the Moseley law.—Following the irregular doublet law, the radiated frequencies resulting from transitions between the terms arising from $3 d 4 p$ and $3 d 4 s$ as well as from transitions between the terms arising from $3 d 4 d$ and $3 d 4 p$ in going from element to element are displaced to higher and higher frequencies by very nearly a constant frequency interval. The combination of ordinary energy level diagrams with a Moseley diagram brings out a number of interesting relations between the iso-electronic systems K I, Ca II, Sc III, Ti IV and V V, and the iso-electronic systems Ca I, Sc II, Ti III, V IV and Cr V. The Moseley diagram and the irregular doublet law served admirably in determining the approximate positions of the various singlet and triplet levels as well as the approximate location in the spectrum of the radiated frequencies.

Landé interval rule; Hund's rule.—The triplet term separations follow fairly well the Landé interval rule. In general Hund's rule is valid for low lying terms in each spectrum. One violation, however, in the middle terms should be mentioned namely; the ${}^{1}D_{2}$ term arising from the electron configuration $3 d 4 p$ lies deeper than the triplet terms. The ionization potentials, that is the voltage necessary to remove one $3 d$ electron from the normal state ${}^{3}F_{2}^{'} (3 d^{2})$ of V IV and Cr V, to the normal state ${}^{2}D_{2} (3 d)$ of the once more ionized atoms are determined at about 48.3 volts and 72.8 volts respectively.

Received 19 December 1928

DOI:https://doi.org/10.1103/PhysRev.33.538

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