Spectral Relations between Certain Iso-electronic Systems and Sequences. Part II; Sc I, Ti II, V III, Cr IV, and Mn V

The spectra of doubly ionized vanadium, V III, triply ionized chromium, Cr IV, and quadruply ionized manganese, Mn V.---The neutral atoms of vanadium chromium, and manganese in the normal state contain five valence electrons, 3d³4s², six valence electrons, 3d⁵4s, and seven valence electrons, 3d⁵4s², respectively. The removal of two electrons, 4s², from vanadium, of three electrons, 3d²4s, from chromium, and of four electrons, 3d²4s², from manganese yields three iso-electronic systems, V III, Cr IV and Mn V, the lowest energy levels of which arise from the three remaining electrons, 3d³. The spectra of these three elements so ionized resemble very closely the spectra of neutral scandium and of singly ionized titanium. Extrapolations from the already known data of Sc I, and Ti II, have led to the identification of terms arising from the electron configurations 3d³, 3d²4s, 3d²4p, and 3d²4d, for V III, Cr IV and Mn V.The irregular doublet law.---Following the irregular doublet law the radiated frequencies resulting from transitions between the terms arising from 3d²4p and 3d²4s as well as combinations between the terms arising from 3d²4d and 3d²4p 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 Sc I, Ti II, V III, Cr IV, and Mn V and the two sequences of iso-electronic systems starting with K I and Ca I, respectively. The Moseley diagram and the irregular doublet law are the chief guides in determining approximately the positions of the various doublet and quartet levels as well as the approximate location in the spectrum of the radiated frequencies.Land\'e's interval rule and Hund's rule.---The quartet term separations follow fairly well the Land\'e interval rule, examples of which are given. In general Hund's rule for relative term positions is valid for low lying terms in each spectrum.Ionization potentials.---The ionization potentials, that is the voltage necessary to remove one $3d$ electron from the normal state a⁴F₂^'(3d³) of V III, Cr IV, and Mn V, to the normal state a³F₂^'(3d²) of the once more ionized atoms, are determined at about 29.6 volts, 50.4 volts, and 75.7 volts respectively.