Knowledge Bank

The interpretation of the lowest Rydberg states of NO given recently by Huber and $Miescher1$ has been fully confirmed by the identification in the absorption spectrum, of several higher members of the proposed Rydberg $series.2$ The exceedingly complex spectrum can now be interpreted, owing to the work of Miescher and his $collaborators,3$ in terms of a relatively simple electronic energy level diagram. The pattern of Rydberg states resembles strongly that of an atom with closed-shell core. The molecular states corresponding to atomic p- and d- states split into components with different $\lambda$, but in NO the sign of this splitting is opposite to the one expected and found in Rydberg states of $H2+,H2,He2,N2$, and CO. The pattern observed in NO has been reproduced rather well in the recent theoretical calculation by LeFebvre-Brion and $Moser4$ who have taken into account the configuration interaction between the unoccupied (Rydberg-) orbitals though they have not included the interaction with excited valence-shell configurations. The relative absorption intensities of the Rydberg bands and the interactions with non-Rydberg states are well explained by the assignment of approximate $g-$ and $u-$ symmetries to the states of the nearly symmetric NO molecule. The $p-$ type Rydberg states of configurations $np\sigma u$ and $np\pi u$ appear with much greater absorption intensities than those resembling atomic $s-$ and $d-$ states and they interact strongly with the non-Rydberg states $\mathrm{<mrow\; data-mjx-texclass="ORD">2</mrow>}Hu$ and with the repulsive state $(\sigma u2p)2\Sigma u+$. These and other observations confirm that it is meaningful to describe the lowest Rydberg states of NO with quantum numbers 3s, 3p, 3d of an atom with a closed $n=2$ -shell core such as Boron or Sodium.