On highly excited electronic states of the NO molecule reached by multiphoton spectroscopy

A recent multiphoton experiment by Wallace and Innes involves an energy level of the NO molecule that belongs to a very interesting sequence of rovibronic states in which an np Rydberg complex (C 2Π+D 2Σ+, v = 6) and a regular and inverted valence state (B 2Πr, v = 24 and L 2Πi, v = 5) are strongly mixed with each other. This multistate interaction, which is typical for highly excited molecular states reached in multiphoton spectroscopy, is discussed as an unique example of a nontrivial case of Rydbergization of valence states. Gallusser’s vibronic coupling calculation and new interpretations of local perturbations in three different isotopes are used to establish the absolute vibrational numbering and the deperturbed rovibronic and spin–orbit constants of the L 2Πi state which had been poorly known previously.