Magnetic Rotation Spectrum of the Red Bands of Sodium

The magnetic rotation spectrum of the red bands of sodium shows a large number of doublets. A doublet is interpreted as made up of an $R$-branch and a $P$-branch line having a common upper $K^{\prime }$ rotational level. The $K^{\prime }$ values for the doublets are calculated and it is found that the rotational levels in the various initial vibrational states from 0-12 which give rise to magnetic rotation doublets are 53, 45, 33, 14, 60, 52, 43, 31, 16, 58, 51, 40, 28 respectively. That just these levels give rise to magnetic rotation lines suggests that these levels are perturbed. Since a ${}_{}{}^3{}_{}{}^{}\Pi$ state is predicted to lie below the upper ${}_{}{}^1{}_{}{}^{}\Sigma$ state we have perhaps here evidence of a perturbation between a ${}_{}{}^1{}_{}{}^{}\Sigma$ and a ${}_{}{}^3{}_{}{}^{}\Pi$ state. To account for the magnetic rotation doublets it has been necessary to revise the vibrational numbering, increasing the initial state numbering by three.