The Spark Spectrum of Nickel (Ni II)

The analysis of the spark spectrum of nickel shows that the important atomic structures are $d^{8}s$ and $d^{8}p$. The low set of terms comprises ${}_{}{}^4{}_{}{}^{}F_{}^{\prime }{}_{}{}^{}$, ${}_{}{}^2{}_{}{}^{}F_{}^{\prime }{}_{}{}^{}$, ${}_{}{}^4{}_{}{}^{}P_{}^{\prime }{}_{}{}^{}$, ${}_{}{}^2{}_{}{}^{}P_{}^{\prime }{}_{}{}^{}$, ${}_{}{}^2{}_{}{}^{}D$, ${}_{}{}^2{}_{}{}^{}G$ of which ${}_{}{}^4{}_{}{}^{}F_{}^{5\prime }{}_{}{}^{}$ is lowest. The only expected term from the structure $d^{8}s$ which has not been found is ${}_{}{}^2{}_{}{}^{}S$. All the intermediate terms ($d^{8}p$) have been found with the exception of a ${}_{}{}^2{}_{}{}^{}P$, and a doubtful ${}_{}{}^2{}_{}{}^{}F$ and ${}_{}{}^2{}_{}{}^{}S_{}^{\prime }{}_{}{}^{}$. A higher member of the ${}_{}{}^4{}_{}{}^{}F_{}^{\prime }{}_{}{}^{}{}_{}{}^2{}_{}{}^{}F_{}^{\prime }{}_{}{}^{}$ series ($d^8, s$) has been found and indicates an I.P. of 17.4 volts from $d^{8}s$ to $d^8$. The expected lowest term ${}_{}{}^2{}_{}{}^{}D\left(d^9\right)$ has not been found. Terms are inverted with the following exceptions: (1) $a{}_{}{}^4{}_{}{}^{}G_{}^{6\prime }{}_{}{}^{}$ is higher than $a{}_{}{}^4{}_{}{}^{}G_{}^{5\prime }{}_{}{}^{}$, (2) $a{}_{}{}^4{}_{}{}^{}P_{}^{3\prime }{}_{}{}^{}$ is higher than $a{}_{}{}^4{}_{}{}^{}P_{}^{1\prime }{}_{}{}^{}$, (3) $b{}_{}{}^4{}_{}{}^{}D_{}^{4\prime }{}_{}{}^{}$ is higher than $b{}_{}{}^4{}_{}{}^{}D_{}^{1\prime }{}_{}{}^{}$, (4) triad $b{}_{}{}^2{}_{}{}^{}P$, $D^{\prime }$, $F$ is not inverted. Zeeman effects give some irregular $g$-values, but the $g$-sum rule is apparently satisfied. The $g$-sum rule is found to be not confined to terms built on the same ion term.