Rydberg molecule in a magnetic field

Rydberg states of the NO molecule have been probed by two-color resonantly enhanced multiphoton ionization in a magnetic field of 0.93 T. Penetrating s and d states show strong interactions with the intramolecular field while nonpenetrating f states show stronger interactions with the extemal magnetic field. Competition between the molecular core anisotropy and the extemal field anisotropy leads to a greater variety of situations than in a Rydberg atom, ranging from a « weak field » regime to a « strong field » regime. These different situations are illustrated by a multichannel quantum defect calculation on the np states of NO including the Zeeman effect. An extreme situation can be achieved in which the Rydberg molecule looses its molecular character and shows an almost pure atomic structure within each rotational channel.