Pauli Exclusion Principle Required for H₂ + H• Atom Transfer Barrier in Collinear Geometry

The study extends energy-component decomposition of chemical bonds to isolate the kinetic-energy contribution arising from antisymmetrization. In the collinear H₃ system the barrier height collapses to zero when the Pauli term is omitted while nuclear and Coulomb contributions remain, showing the barrier is not a classical electrostatic effect. Absolutely-localized molecular orbital analysis independently confirms the same necessity.

This finding aligns with earlier energy-decomposition work on SN2 and Diels-Alder barriers (Bickelhaupt & Houk, 2017; Angew. Chem.) that attributed activation strain largely to Pauli repulsion, yet those studies did not test barrier disappearance upon explicit removal of the exclusion term. The present calculation supplies that direct test for the simplest atom-transfer case.

If the result generalizes, computational models of hydrogen-transfer catalysis and materials diffusion could replace empirical barrier fits with Pauli-corrected kinetic-energy functionals, potentially improving rate predictions within 12 months. Full peer review and replication on non-collinear geometries remain pending.