Guided ion beam studies of the state-specific reactions of Fe⁺(⁶D,⁴F) with CH₃X (X = Cl, Br, I)

Reactions of Fe⁺ with CH₃X (X = Cl, Br, I) are studied by guided ion beam techniques. State-specific reaction cross sections for production of FeCH₃⁺ and FeX⁺ are presented for the ⁶D ground and the ⁴F first excited states of Fe⁺. The overall behavior seen in these reactions is similar to that seen in the analogous reactions of Co⁺ and Ni⁺, discussed in the preceding paper in this issue. The two states of Fe⁺ exhibit large differences in reactivity, with the ⁴F state generally being more reactive than the ⁶D state for production of FeX⁺ and FeCH₃⁺. The only exception is for the exothermic formation of FeCH₃⁺ below 0.7 eV in the CH₃I system. We postulate that this is due to a potential energy surface crossing that is avoided at low kinetic energies due to spin-orbit interactions and is permitted at higher energies. Analysis of the threshold behavior of the endothermic reactions provides two determinations of D°(Fe⁺-CH₃) = 2.49 ± 0.13 and 2.47 ± 0.07 eV, in good agreement with previous values. Lower limits are placed on the bond energies for Fe⁺-X.