High-resolution threshold photoelectron spectroscopy of molecular fluorine

The threshold photoelectron spectrum of molecular fluorine has been recorded in the 15.6-21.9 eV photon energy range, at resolutions ranging from 3 to 12 meV, using synchrotron radiation and a penetrating-field electron spectrometer. In addition to observing the three known band systems of F-2(+) at higher resolution than previously achieved with conventional photoelectron spectroscopy, extensive vibrational structure is found in the Franck-Condon gaps between the main electronic systems of F-2(+). This extended vibrational structure is attributed to resonance autoionization of neutral Rydberg states.