Potassium ground state scattering parameters and Born-Oppenheimer potentials from molecular spectroscopy
Abstract
We present precision measurements with MHz uncertainty of the energy gap between asymptotic and well bound levels in the electronic ground state X 1g+ of the 39K2 molecule. The molecules are prepared in a highly collimated particle beam and are interrogated in a -type excitation scheme of optical transitions to long range levels close to the asymptote of the ground state, using the electronically excited state A 1+ u as intermediate one. The transition frequencies are measured either by comparison with I2 lines or by absolute measurements using a fs-frequency comb. The determined level energies were used together with Feshbach resonances from cold collisions of 39K and 40K reported from other authors to fit new ground state potentials. Precise scattering lengths are determined and tests of the validity of the Born-Oppenheimer approximation for the description of cold collisions at this level of precision are performed.