State-specific reactions of Fe⁺(⁶D, ⁴F) with O₂ and c-C₂H₄O: D°₀(Fe⁺-O) and effects of collisional relaxation

Reactions with Fe⁺ with O₂ and c-C₂H₄O are studied by guided ion beam techniques. State-specific reaction cross sections for production of FeO⁺ are presented for the ⁶D ground and the ⁴F first excited states of Fe⁺. In the reaction with O₂, these states exhibit similar cross section energy dependences and magnitudes, in contrast to large differences noted with H₂. The dissimilarities are explained in terms of spin and orbital considerations that are much less restrictive in the case of reaction with the triplet O₂ molecule. With ethylene oxide, Fe⁺(⁶D) reacts endothermically to form FeO⁺, while Fe⁺(⁴F) shows exothermic behavior. The clear difference in cross section behaviors allows a precise determination of D°₀(Fe⁺-O) = 3.53 ± 0.06 eV. This derived value is discussed with respect to several past results. Also presented is reaction of O₂ with Fe⁺ created by laser vaporization. A small fraction of the ions produced by this source is not completely quenched by >10⁵ collisions with He. The extent of this residual electronic excitation is found to be dependent on the power of the vaporizing laser.