An electronic absorption spectrum of FO has yet to be observed experimental
ly but as a guide for future spectroscopic studies of this radical, CASSCF/
MRCI ab initio calculations have been performed to locate and identify the
lowest energy valence and Rydberg states. No bound valence excited potentia
ls were found save the a(4)Sigma(-) state. The calculations provide estimat
es of the transition energies T-e to the lowest Rydberg states and the wave
lengths required for spectroscopic detection. Results for both the doublet
and quartet states are presented, revealing the 3s sigma, 3p pi, 3p sigma,
3d delta, 4d sigma, 3d pi, and 4d delta Rydberg orbitals. It is likely that
the repulsive valence states 1(2)Sigma(-) and 1(2)Delta predissociate the
lowest Rydberg states of the same symmetry. Consequently, the 2 Pi Rydberg
states, three of which are found here, are the most promising candidates fo
r optical detection.