Knowledge Bank

The rotational structure of one band in the electronic transition of the $HCN2$ free radical near 3170 A has been measured. This spectrum was first reported by Herzberg and $Travis1$ in their paper on the NCN radical. The complexity of the fine structure required an iterative approach. First and second differences were used in the assignments of J values and a correlation performed with the computed line diagram. The observed transitions were subjected to a least squares fit to calculate a new theoretical spectrum. This was repeated until the best fit of the molecular constants was achieved. The resulting geometries for both the upper and lower electronic states are then compared with the results of ab initio calculations for HCNN.