SPIN-ORBIT-COUPLING IN THE OXIDATIVE ACTIVATION OF H-H BY FEO- SELECTION-RULES AND REACTIVITY EFFECTS( )

Spin-orbit coupling (SOC) calculations are performed along the reactio n pathway of the oxidation process, FeO+ + H-2 --> Fe+ + H2O (eq 1). S election rules are derived for SOC between different spin situations, and are applied to understand the computed SOC patterns along the oxid ation pathway, and their relationship to the electronic structure of t he various species. The process involves two spin inversion (SI) junct ions between sextet and quartet states: near the FeO+/H-2 cluster at t he entrance channel, and near the Fe+/H2O cluster at the exit channel. The sextet-quartet SOC is significant at the reactant extreme (for Fe O+), but decreases at the FeO+/H-2 cluster and continues to decrease u ntil it becomes vanishingly small between the D-6-F-4 states of Fe+ at the product extreme. The results show that while the quartet surface provides a low-energy path, the SI junctions reduce the probability of the oxidation process significantly. In agreement with the deductions of Armentrout et al., (2c) the poor bond activation capability of the D-6 ground state of Fe+ in the reverse reaction is accounted for by t he inefficient D-6-F-4 State mixing due to the expected poor SOC betwe en the respective 4s(1)3d(6) and 3d(7) configurations. On the other ha nd, the F-4 excited state of Fe+ can activate H2O more efficiently sin ce it can lead to the insertion intermediate (4)(HFeOH+) in a spin-con serving manner. Other findings of Schwarz et al.(1,2a) and Armentrout et al.(2c,d) are discussed in the light of the SOC patterns. The impor tance of the SOC at the exit channel is highlighted by comparing the p roduct distribution of the reaction (eq 1) with analogous reactions of MO(+) species: when the ground state M(+) has a 4s(1)3(n-1) (Fe+, Mn) electronic structure as opposed to those cases where the ground stat e electronic structure is 3d(n) (Co+, Ni+) and where no spin inversion is required. Predictions based on the understanding of the SOC patter ns are made and compared with appropriate experimental data.