Rydberg state

An electronic state that arises by the excitation of a valence electron to a diffuse atomic-like orbital. For instance, the lowest lying Rydberg state (n, 3S) of NH3 can be described as resulting from the excitation of a non-bonding orbital to a 3S Rydberg orbital.
PAC, 1999, 71, 1919 (Glossary of terms used in theoretical organic chemistry) on page 1961