Depletion of FeO in the interstellar medium through resonance states of FeO⁻ was studied through collisioninduced dissociation of FeO⁻. Collisional excitation of FeO⁻ lead to the yield of Fe⁻ and O⁻, with a higher yield for Fe⁻. The ground electronic state of FeO⁻ was identified to be ⁶Δ state and the results are compared with previous theoretical and experimental results. The kinetic energy distributions of the fragments revealed two FeO⁻ anion resonances accessed upon excitation and their potential energy curves were evaluated. The role of the observed resonances in the depletion of FeO and the viable presence of Fe⁻ and O⁻ in Sagittarius B2 are discussed.