Communication: Covalent nature of X center dot center dot center dot H2O (X = F, Cl, and Br) interactions

Open-shell halogen (X = F, Cl, Br) atoms form entrance-channel complexes with H2O, which play an important role in the X + H2O reactions. To understand their structures and origin of stability, we report an extensive ab initio study of such complexes and contrast them with complexes between H2O and H/O(P-3). Evidence is presented to show that the interaction between a halogen atom and H2O is dominated by a weak but covalent bond, rather than dispersion and/or electrostatic interactions. (C) 2013 AIP Publishing LLC. [http://dx.doi.org/10.1063/1.4801872]