Knowledge Bank

A number of small diatomic radicals have bound doublet and quartet states. Examples of such systems include $CN,N2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>},C2\mathrm{<mrow\; data-mjx-texclass="ORD">-</mrow>}$, and $O2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$. Since optical selection rules forbid the intercombination of the quartet and doublet states, the excitation energy to the lowest quartet and its structure is usually poorly known. Previously, we have reported doublet-quartet anticrossings in CN, and we now present a description of the fine structure of the $B2\Sigma +$ and $a4\Sigma +$ states of CN based upon an analysis of these anticrossings. We also report newly observed doublet-quartet anticrossings in $O2\mathrm{<mrow\; data-mjx-texclass="ORD">+</mrow>}$.