Rotational Analysis of the 2900A Band of CO2+

A rotational analysis of the C$\mathrm{O}_2^{}{}_{}{}^{+}$ doublet band near $\lambda 2896$ and $\lambda 2882$ has been made. The band was photographed in the third order of the 30-foot grating spectrograph at Ryerson Laboratory with a dispersion of 0.22A/mm and a resolving power of 300,000. The structure is explained by a ${}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_u{}^{}\to {}_{}{}^2{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ (case $a$, inverted) transition, where the ${}_{}{}^2{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ is the ground state of C$\mathrm{O}_2^{}{}_{}{}^{+}$. Alternate lines are missing as expected for ${}_{}{}^2{}_{}{}^{}\Sigma$ in view of the zero spin of the oxygen nuclei. A number of perturbations are observed, which involve displacements and weakening of the lines. These are probably caused by higher vibrational levels of a ${}_{}{}^2{}_{}{}^{}\Pi _u^{}{}_{}{}^{}$ state which lies about 0.8 volts below the ${}_{}{}^2{}_{}{}^{}\Sigma _{}^{+}{}_u{}^{}$. The values found for the molecular constants of the lower ${}_{}{}^2{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ state ($B_1=0.3795\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$, $B_2=0.3813\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and the $\Lambda$-doubling coefficient $p=0.004\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$) agree with those found by Mrozowski. For the upper ${}_{}{}^1{}_{}{}^{}\Sigma _{}^{+}{}_u{}^{}$ state, $B=0.3784\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$ and the spin-doubling coefficient $\gamma =0.019\mathrm{}$ ${\mathrm{cm}}^{-1\mathrm{}}$. The spin-orbit coupling coefficient $A$ for the ${}_{}{}^2{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ state is — 159.5 ${\mathrm{cm}}^{-1\mathrm{}}$.