Vibronic interactions in trilobite and butterfly Rydberg molecules

TL;DR

This paper investigates the breakdown of the Born-Oppenheimer approximation in trilobite and butterfly Rydberg molecules due to strong non-adiabatic couplings, highlighting the necessity of including non-adiabatic effects for accurate modeling.

Contribution

It provides a coupled-channel approach to accurately describe vibronic interactions and non-adiabatic effects in ultralong-range Rydberg molecules, revealing limitations of single-channel models.

Findings

Non-adiabatic trapping and decay near avoided crossings

Single channel models need diagonal non-adiabatic corrections

Non-adiabatic physics is crucial for vibronic spectra interpretation

Abstract

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 non-adiabatic 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 non-adiabatic 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 non-adiabatic corrections to the Born-Oppenheimer potentials. Our results indicate the importance of including non-adiabatic physics in the description of ultralong-range Rydberg molecules and in the interpretation of measured vibronic spectra.