Although the energy formula of Rydberg series is a result of hydrogen-like atom structure, Rydberg states are also present in molecules. Wave functions of high Rydberg states are very diffuse and span diameters that approach infinity.
While the Rydberg formula is based on the structure of hydrogen atoms, it can be applied to molecules as well.  The wave functions for high Rydberg states in molecules are very spread out and extend far beyond typical atomic or molecular dimensions.