The effects of nonadiabatic physics in long-range 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 in the vicinity of pronounced avoided crossings in the adiabatic potential curves. Furthermore, we see how nonadiabatic couplings in a second Rydberg system, a long-range charged molecular ion, contribute to its dissociative decay. Using the same coupled channel treatment developed for the trilobite molecules in addition to an eigenchannel R-matrix approach, we calculate the scattering matrices governing the dissociation and resulting lifetimes. Our results indicate the importance of including nonadiabatic physics in the description of Rydberg molecules and in the interpretation of measured vibronic spectra and lifetimes.