Chlorine and hydrogen chloride on clean and oxygen‐covered Fe(100): Bonding and reactions

An ASED molecular orbital study of the binding, structures, and reactions of Cl, Cl₂, HCl, and HCl+O on 4–21 atom clusters in the Fe(100) structure has been made. Cl₂ bonds dissociatively (as seen by Dowben and Jones in LEED and TDS studies). Coverage is limited by σ^*_p repulsions; orbitals of this symmetry are occupied by electron donation from iron. We find Cl favors onefold and twofold sites and discuss this unexpected result with perturbation theory. It is suggested that with decreased backbonding from iron to Cl the fourfold site can become favored. There is an absence of experimental or theoretical evidence supporting orbital reoccupations to favor the high‐coordinate site. HCl dissociation is found to occur with a barrier on the surface that is roughly half the gas phase binding energy, leading to stable products. The HCl+O→Cl+OH reaction on the surface is found to be structure sensitive and the reasons are interpretable from molecular orbital theory.