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 observati on of the threshold of ionization and of Rydberg series. The Rydberg s eries were observed by field ionization as series that converge to the first ionization limit and as autoionizing series that converge to th e second and to several higher convergence limits. The threshold and R ydberg series were obtained through a number of two- and three-step pa thways. The photoionization threshold value for the Pu-239 I ionizatio n potential is 48582(30) cm-1, and the more accurate value from the Ry dberg series is 48 604(1) cm-1 or 6.0262(1) eV.