High precision spectroscopy of trilobite Rydberg molecules*

In this study, we present high-resolution spectra of ⁸⁷Rb trilobite dimers with principal quantum numbers n in the range of 22 to 27. These exotic molecules exhibit very large permanent dipole moments of nearly 3000 Debye, making them among the most polar molecular systems known. Their substantial binding energies, combined with a relative spectral resolution of 10^-4, provide a stringent test for current theoretical models.

Using a recently developed Green's function framework, we accurately reproduce the vibrational spectra, overcoming previous convergence issues. The molecular binding energies are primarily governed by the low-energy s-wave electron-atom scattering length. This enables us to extract the ³S₁ scattering phase shift with unprecedented precision at low energy regimes, which are inaccessible to free electrons.

Our findings not only provide a powerful benchmark for advancing electron-atom scattering theories but also highlight the unique properties of trilobite Rydberg molecules, including their extreme polarity and high-angular-momentum character.