The Arc Spectrum of Copper

The arc spectrum of coppper is partly an ordinary doublet spectrum with lowest term ${}_{}{}^2{}_{}{}^{}S=62308.0\mathrm{}$; and partly a complicated spectrum with lowest term $m{}_{}{}^2{}_{}{}^{}D_3^{}{}_{}{}^{}=51105.5\mathrm{}$ and $m{}_{}{}^2{}_{}{}^{}D_2^{}{}_{}{}^{}=49062.6\mathrm{}$. The next lowest terms of the complicated spectrum are ${}_{}{}^4{}_{}{}^{}P$, ${}_{}{}^4{}_{}{}^{}F$, ${}_{}{}^4{}_{}{}^{}D_{}^{\prime }{}_{}{}^{}$, ${}_{}{}^2{}_{}{}^{}F$, ${}_{}{}^2{}_{}{}^{}P$, ${}_{}{}^2{}_{}{}^{}D_{}^{\prime }{}_{}{}^{}$ in the order given extending from ${}_{}{}^4{}_{}{}^{}P_3^{}{}_{}{}^{}=23289.4\mathrm{}$ to ${{}_{}{}^2{}_{}{}^{}D_{}^{\prime }{}_{}{}^{}}_3=15709.7\mathrm{}$. They combine with ${}_{}{}^2{}_{}{}^{}S$ and $m{}_{}{}^2{}_{}{}^{}D$. The quartets are all inverted, while the doublets are not. There are eleven higher terms which include amongst others a second set ${}_{}{}^2{}_{}{}^{}F$, ${}_{}{}^2{}_{}{}^{}P$, ${}_{}{}^2{}_{}{}^{}D_{}^{\prime }{}_{}{}^{}$. This is all as predicted by the Heisenburg-Hund theory. Most of the lines of the arc spectrum are due to the combinations of the above quartets and doublets with a set of terms having negative wave-numbers extending from -95.2 to -14772.4. In particular, the lowest four negative terms are a complete ${}_{}{}^4{}_{}{}^{}D$ and form by combination with ${}_{}{}^4{}_{}{}^{}P$, ${}_{}{}^4{}_{}{}^{}F$, ${}_{}{}^4{}_{}{}^{}D_{}^{\prime }{}_{}{}^{}$ multiplets of great intensity in the visible. The other negative terms include a set ${}_{}{}^4{}_{}{}^{}S$, ${}_{}{}^4{}_{}{}^{}P_{}^{\prime }{}_{}{}^{}$, ${}_{}{}^4{}_{}{}^{}D$, ${}_{}{}^4{}_{}{}^{}F_{}^{\prime }{}_{}{}^{}$, ${}_{}{}^4{}_{}{}^{}G$, which also combine with considerable intensity with the first mentioned quartets. The limit of the negative quartet terms can be calculated to be at roughly -22,000. This should be the lowest spark ${}_{}{}^3{}_{}{}^{}D$ term.