Quantum chemical computations were applied to investigate the characteristics of open-shell hydrogen-bonding interactions in the complexes of carbamic acid (NH 2 COOH, CA) with HO 2 , HOS and HSO radicals. All the resulting complexes were studied using the MP2, B3PW91 and B3LYP computational levels and 6311++G** basis set. Geometry optimizations show that the O– H⋯O contact is stronger than N–H⋯O and S–H⋯O. The interaction energies revealed that all the radicals form stronger hydrogen bonded complexes at site-1, as confirmed by electron-density (ρ) and corresponding Laplacian (∇ 2 ρ) values obtained by atoms in molecule (AIM) analysis. Non-covalent interaction and reduced density gradient analysis support the AIM results. Natural bond orbital analysis was employed to obtain the stabilization energies (E (2) ) due to charge delocalization between the interacting units. Energy decomposition analysis suggests that, for the title complexes, the exchange energy makes a larger contribution to the total interaction energy compared to other energy terms.
