Rydberg Series in the NO Spectrum: An Interpretation of Quantum Defects and Intensities in the s and d Series

The observed quantum defects in the s and d Rydberg series of NO are interpreted. It has been shown previously that the nf Rydberg states of NO conform to a long-range force model. This model assumes that the motion of the Rydberg electron is determined only by the long-range potential of the NO+ core. The same model, when applied to the nd states, fails to reproduce the observations. The differences between predicted and observed energies result from: (i) exchange effects and increased nuclear attraction inside the core, (ii) the required orthogonality of the wavefunction of the Rydberg electron with respect to core electrons, (iii) mixing of the dσ with the sσ Rydberg series. In order to describe these effects (called penetration effects) quantitatively, the long-range force model is supplemented by additional parameters. These parameters are determined independently from the observed electronic and from the observed rotational energy level patterns, and good agreement is found. The mixing of the dσ with the sσ Rydberg series is shown to influence strongly the intensities of numerous transitions in the near infrared, in the visible and in the ultraviolet spectral regions. Numerical calculations for the core orbitals of NO support this interpretation of the penetration effects. The possible assignments of “atomlike” quantum numbers to a molecular Rydberg orbital are discussed.