The one-optical-electron spectrum of the free ion U5+ (U VI) has been analysed between 50 and 210 nm, and the eight transitions which connect the 5f, 6d, 7s and 7p configurations have been found (76.5).
The first excited configuration predicted by the Hartree-Fock method in the odd parity is 6p55f2, which has not yet been located. None members of the Rydberg series being known, the ionization limit cannot be derived from the observed spectrum.