The ultraviolet photoelectron spectrum of F2O was recorded with a higher resolution than previously published. New vibrational structure was observed in the second and third bands. Near state-of-the-art molecular orbital calculations were performed on the 1A1 state of F2O and the 2B1, 2B2, 2A1, and 2A2 state of F2O+, and their potential energy functions were computed. Spectral simulations based on Franck–Condon factor calculations including the Duchinsky effect were carried out within the harmonic oscillator model and also with the inclusion of anharmonicity, in order to assist spectral assignment. Based on the computed ionization energies obtained with the coupled cluster and multireference configuration interaction methods with basis sets of up to quintuple zeta quality, the order of the low-lying cationic states of F2O+ has been firmly established. However, the detailed assignment of the overlapping second and third photoelectron bands was only achieved with the aid of spectral simulation. The iterative Franck–Condon analysis (IFCA) procedure was carried out for the first band {F2O+ ( 2B1)←F2O ( 1A1)} in the photoelectron spectrum. With the geometrical parameters of F2O ( 1A1) being fixed at the available experimental values, geometrical parameters of the 2B1 state of F2O+ were derived. Based on anharmonic Franck–Condon factor calculations, the recommended IFCA geometrical parameters for the ground state of F2O+ are R(FO) = 1.323±0.002 Å and ∠FOF = 107.3±0.2°. © 2001 American Institute of Physics.