Knowledge Bank

The CN radical is one of the most studied molecules. Nine doublet states of the molecule are known from optical spectroscopy. No direct observation of a quartet state has ever been made; however, recent experiments by Coxon, Ramsay, and $Setser1$ strongly indicate that a quartet state is responsible for the perturbation of the N = 20, v = 11 levels of the $B2\Sigma +$ state. Recent experiments by ourselves have shown the power of the anticrossing method for the study of the forbidden singlet-triplet spectroscopy of $H2,D2$ and $He2$. Using the Ar metastable method for producing CN we have performed an anticrossing experiment on the N = 20, v = 11 level of $B2\Sigma ++CN$. Strong, structured increases in optical emission as a function of magnetic field have been observed. These are interpreted as due to the magnetically tuned anticrossings between first the $MS=3/2$ and then $Ms=1/2$ levels of the quartet state with the two rho doublets of the N = 20 level of the $B2\Sigma +$ state. The basic anticrossing structure is rather broad but superimposed upon it are quite narrow lines ( gauss) which we tentatively attribute to forbidden anticrossings. Details will be presented concerning the doublet-quartet zero field splitting, spin splitting in the quartet, etc.