Extension of the Analysis of Singly Ionized Gadolinium (Gd ii)*

Energy levels belonging to a system of three newly identified configurations of singly ionized gadolinium are established. This system is obtained by adding to the ⁷F term of the 4f⁸ core the 6s, 6p, and 5d electrons. The lowest level of this system, designated at ${{}^{8}F}_{6\frac{1}{2}}$ of 4f⁸(⁷F)6s, lies 7992.31 cm⁻¹ above the $4f^7({}^{8}S)5d6s^{10}{D}_{2\frac{1}{2}}°$ ground level. Transitions connecting the new system to the ground configuration strictly obey the selection rule ΔS_I = 0, where S_I is the parent spin. Coupling calculations furnish the theoretical basis for this selection rule and explain the unusual intensity relations found experimentally in the infrared. Energy levels for the 4f⁸(⁷F)5d and 4f⁸(⁷F)6p are designated in L–S and J–J coupling, respectively. Best values for the radial parameters of 4f⁸(⁷F)6p are obtained by least-squares calculation, with an rms error of 197 cm⁻¹. About 300 lines are classified.