Vibronic interactions in trilobite and butterfly Rydberg molecules

Ultralong-range Rydberg molecules provide an exciting testbed for molecular physics at exaggerated scales. In the so-called trilobite and butterfly Rydberg molecules, the Born-Oppenheimer approximation can fail due to strong nonadiabatic couplings arising from the combination of radial oscillations and rapid energy variations in the adiabatic potential energy curves. We utilize an accurate coupled-channel treatment of the vibronic system to observe the breakdown of Born-Oppenheimer physics, such as nonadiabatic trapping and decay of molecular states found near pronounced avoided crossings in the adiabatic potential curves. Even for vibrational states localized far away from avoided crossings, a single-channel model is quantitatively sufficient only after including the diagonal nonadiabatic corrections to the Born-Oppenheimer potentials. Our results indicate the importance of including nonadiabatic physics in the description of ultralong-range Rydberg molecules and in the interpretation of measured vibronic spectra.

Automated summary

Ultralong-range Rydberg molecules offer a valuable platform for studying molecular physics on a large scale. Nonadiabatic effects, resulting from radial oscillations and rapid energy variations in the adiabatic potential energy curves, can cause the breakdown of the Born-Oppenheimer approximation in trilobite and butterfly Rydberg molecules. Using a coupled-channel model, we observed nonadiabatic trapping and decay of molecular states near avoided crossings in the adiabatic potential curves. Our results highlight the significance of including nonadiabatic physics in the description and interpretation of ultralong-range Rydberg molecules.