Intramolecular electronic and rotational angular momentum coupling in ⁸⁴Sr ¹D₂ ultralong-range Rydberg dimers

We use photoassociative spectroscopy to study ⁸⁴Sr ¹D₂ ultralong-range Rydberg molecule (ULRRM) dimers and develop a model incorporating diabatic rovibrational mixing. The measured binding energies are fit well by theory, yielding s-wave and p-wave electron-atom scattering parameters a_s = -13.84 a₀ and a_p = 9.7 a₀, where a₀ is the Bohr radius, consistent with previous studies of ³S₁ Rydberg dimers. Excitation in the zero-temperature limit will only populate K = 2 molecular states, where K=L+N is the sum of the electronic and rotational angular momenta. At the finite temperature of the experiment, higher partial-wave initial scattering channels become populated, leading to rotational-state mixing and the appearance of additional even-K molecular states, including K = 0 and K = 4. Finally, we investigate the effect of an applied magnetic field and the transition between the weak-field regime, in which electron-atom scattering is the dominant energy scale and the projection of the electronic orbital angular momentum along the molecular axis (\Lambda =0) is well defined, to the strong field regime governed by the Zeeman interaction.