In other words, the condition of limited overlap between half-filled orbitals implicated on the catalytic active site and atomic hydrogen is an important aspect of this interaction. When there is maximal overlap on both orbitals, a strong covalent bond is formed. If there is no overlap on both orbitals, it will be difficult to link the atomic hydrogen on the catalytic active site. Importantly, this weak orbital interaction can arise even if there is a relative difference in energy between two orbitals (such as halffilled s-orbital can interact with half-filled d-sub-orbital via limited overlap).