Quadratic Zeeman effect in Rydberg states of NO

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 range 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.