We analyse a resonant-enhanced multiphoton ionization (REMPI) spectrum of the high n (35-50) members of the Rydberg series of NO molecules recorded in a 1 T external magnetic field. In this range the quadratic Zeeman interaction takes over the Coulomb interaction and gradually scrambles the Coulomb structure of the Rydberg series. A perturbative quantum treatment of the diamagnetic interaction, giving rise to the so-called l-mixing and n-mixing, shows that the apparent complexity of the higher

more »

... ange of the experimental spectra results essentially from the interplay of two Rydberg series associated with different rotational core states. This perturbative treatment is expected to gradually break down and a semiclassical approach is proposed to understand the underlying physical pattern governing this higher spectral range.