Bonding Nature of Diabatic Representation in Nonlinear Hydrogen Atom Transfer Reactions

The construction of diabatic representations is important for understanding nonadiabatic processes. Significant efforts have been devoted to developing robust and generalizable methodologies for diabatization, aiming to improve numerical accuracy, computational efficiency, and transferability across diverse systems. However, while substantial progress has been made on the methodological front, the fundamental chemical significance inherent to the diabatic representation itself has received less attention. In this study, we move beyond these technical performance metrics to decode the chemical meaning of diabatic representations in a series of nonlinear (bent) hydrogen atom transfer (HAT) systems. Using classical valence bond (VB) theory, we explicitly analyze the bonding nature (e.g., covalent, ionic) embodied by diabatic representation in model HAT systems (H₃, H₂F, NaH₂, NaHF, BeH₂⁺), revealing the specific electronic reorganization captured during the reaction. This mechanistic insight extends the traditional diabatic state representation and underscores the role of dynamic bonding pattern mixing.