Ionization potential of neutral atomic plutonium determined by laser spectroscopy

The ionization potential of the neutral plutonium atom, Pu i, has been determined by two- and three-step resonance photoionization observation of the threshold of ionization and of Rydberg series. The Rydberg series were observed by field ionization as series that converge to the first ionization limit and as autoionizing series that converge to the second and to several higher convergence limits. The threshold and Rydberg series were obtained through a number of two- and three-step pathways. The photoionization threshold value for the 239Pu i ionization potential is 48582(30) cm−1, and the more accurate value from the Rydberg series is 48604(1) cm−1 or 6.0262(1) eV.