Beyond-Born-Oppenheimer effects in sub-kHz-precision photoassociation spectroscopy of ytterbium atoms

Abstract

Low-lying rovibrational levels of Yb${}_{2}$ molecules are measured by photoassociation to an accuracy of about 500 Hz. The measurements, in combination with a potential model that includes some beyond-Born-Oppenheimer effects, produce a determination of the $s$-wave scattering lengths with error bars which are over two orders of magnitude better than previous determinations.