The title cation and molecules have been prepared by reactions of laser-ablated metal cations and atoms with NO during condensation in excess neon at 4 K. Infrared fundamentals for the NUO and NThO molecules blue shift 1.6%-2.9% on going from argon to neon matrices and are calculated from 5.8% to 0.0% too high using density functional theory, GAUSSIAN 98, and pseudopotentials on the actinide metal. The isolated NUO+ cation, formed in previous gas-phase ion-molecule reactions, is characterized by new 1118.6 and 969.8 cm(-1) neon matrix absorptions. Two normal modes (isotopic frequencies) are accurately modeled by the calculations for NUO+, NUO, and NThO. The isolated NUO+ cation observed here provides a vibrational model for its important isoelectronic UO22+ analog, which has only been characterized in condensed phases where partial neutralization of the dication readily occurs.