The intermolecular interactions of ammonia with chlorine and bromine oxides: a theoretical study

The role of halogen oxides is substantial in the stratosphere, especially for ozone depletion. It is important to make clear the interaction of halogen oxides with other gaseous molecules. This work performed quantum chemical calculations to investigate the intermolecular interactions between X_mO_n (X = Cl or Br, m, n = 1 or 2) and ammonia. The chlorine and bromine oxides selected in this paper include typical halogen oxides which can influence the atmospheric processes. For each complex, two different types of interactions, halogen and hydrogen bonds were identified. A π-hole interaction was also found in the XO₂···NH₃ complex. The interaction energy implies that the strength of the halogen bond is far more stronger than the hydrogen bond. A prominent difference exists between the halogen oxides of singlet or doublet state, which can be ascribed to the electron spin density distribution. The nature of the intermolecular interactions was identified by an independent gradient model based on Hirshfeld partition (IGMH) analysis. Symmetry-adapted perturbation theory (SAPT) calculation indicates that electrostatic interaction dominates the halogen-bonded complex, and hydrogen bond is driven by electrostatic interaction and dispersion.