result, any isolated neutral molecule behaves like a hydrogen-like atom at the Rydberg limit. For molecules with multiple stable monovalent cations, multiple Rydberg series may exist. Because of the complexity of molecular spectra, low-lying Rydberg states of molecules are often mixed with valence states with similar energy and are thus not pure Rydberg states. See also Rydberg atom Rydberg matter Orbital state References Atomic Spectra and Atomic Structure, Gerhard Herzberg, Prentice-Hall, 1937. Atoms and Molecules, Martin Karplus and Richard N. Porter, Benjamin & Company, Inc., 1970. External links Army Creates Quantum Sensor That Detects Entire Radio-Frequency Spectrum; Defense One. Rydberg Atoms and the Quantum Defect; Physics Department, Davidson College. Rydberg state; Science Direct. Rydberg Transitions; Chemistry and Biochemistiry, Georgia Tech. Atomic physics Atomic, molecular, and optical physics