The electronic spectroscopy of UO2 has been examined using multiphoton ionization with mass-selected detection of the UO2+ ions. Supersonic jet cooling was used to reduce the spectral congestion. Twenty-two vibronic bands of neutral UO2 were observed in the range from 17 400 to 32 000 cm(-1). These bands originated from the U(5fphi(u)7ssigma(g))O-2 X (3)Phi(2u) and (3)Phi(3u) states. The stronger band systems are attributed to metal-centered 7p<--7s transitions. Threshold ionization measurements were used to determine the ionization potentials of UO and. UO2. These were found to be higher than the values obtained previously from electron impact measurements but in agreement with the results of recent theoretical calculations. (C) 2004 American Institute of Physics.