Resonance between electronic and rotational motions in Rydberg states of CaF

Abstract

The interaction between electronic and rotational motions in the Rydberg states of calcium monofluoride is investigated using multichannel quantum defect theory (MQDT). By examining the partial-ℓ and N + composition of the molecular wavefunctions of successive members of each of the Rydberg series, we show that the nature of the interaction between the motion of the Rydberg electron and the rotational motion of the ion core undergoes complex and non-monotonic changes with increasing principal quantum number n* and total angular momentum N. Resonances between the Kepler motion of the Rydberg electron and the rotational motion of the ion core (the ‘stroboscopic effect’) are observed when the Kepler period is an integer multiple of the rotational period. These resonances result in strong mixing of both the electron orbital angular momentum ℓ and the ion core rotational angular momentum N +. At n* or N values between these resonances, the angular momenta of the electron and ion core subsystems are more nearly conserved. We also find evidence for a second type of resonance, which takes place between the precessional motion of the Rydberg electron and the rotation of the core. The qualitative features of these various dynamical regimes can be explained in terms of the classical frequencies of motion of the electron and ion and the nature of the electrostatic interactions between them. The results presented here provide general insights into the interaction between electronic and rotational motions in both polar and non-polar diatomic molecules.