After reactions of uranium atoms with NF3 and PF3 to form the N UF3 and P UF3 molecules, the analogous reaction with AsF3 produced the novel terminal arsenide As UF3. This first molecule with a uranium-arsenic bond was identified from matrix infrared spectra through comparison with spectra of the uranium nitride and phosphide species, with spectra using other metals, and with frequencies computed by density functional and multiconfigurational wave function methods. The latter calculation describes a weak triple bond to uranium in the As UF3 molecule, which has slightly less bonding and more antibonding character than the weak triple bond in P UF3.