Knowledge Bank

Non-penetrating Rydberg states (with large orbital angular momenta $\ell$) in molecules are essentially hydrogenic, except for the weak interaction between the electron and the core's polarizability and its quadrupole $moment.1$ Using the $\ell$-uncoupling representation (Hund's coupling case d), we show that each Rydberg level is first split into N rotational levels of the core, which in turn separate into sub levels labelled by $K(K=\ell \to +K\to )$. Transition frequencies and strengths of the type 4f=5g are evaluated for some homopolar molecules, $H2$ and $N2$, in analogy to those in atomic $nitrogen.2$ Finally, this theory will be compared with the $""\ell structure""theory3$ of Dressler et al.