Nonadiabatic interaction effects in the spectra of ultralong-range Rydberg molecules

Ultralong-range Rydberg molecules (ULRMs) are highly imbalanced bound systems formed via the lowenergy scattering of a Rydberg electron with a ground-state atom. We investigate for Na-23 the d state and the energetically close-by trilobite state, exhibiting avoided crossings that lead to the breakdown of the adiabatic Born-Oppenheimer (BO) approximation. We develop a coupled-channel approach to explore the nonadiabatic interaction effects between these electronic states. The resulting spectrum exhibits stark differences in comparison to the BO spectra, such as the existence of above-threshold resonant states without any adiabatic counterparts, and a significant rearrangement of the spectral structure as well as the localization of the eigenstates. Our study motivates the use of Na-23 ULRMs, as a probe to explore vibronic interaction effects on exaggerated timescales and length scales.

Automated summary

In this study, we investigate the nonadiabatic interaction effects between the d state and the trilobite state of Na-23, and find significant differences in comparison to the adiabatic Born-Oppenheimer approximation. The resulting spectrum exhibits above-threshold resonant states without adiabatic counterparts, and a rearrangement of the spectral structure as well as the localization of the eigenstates. Our study suggests the use of Na-23 ULRMs as a probe to explore vibronic interaction effects on exaggerated timescales and length scales.