MP2 and M05-2x calculations with two basis sets, 6-311++G(2d, 2p) and aug-cc-pVTZ, were used to analyze the interaction between nitrosyl hydride (HNO) and ozone. Four minima were located on the potential energy surface of HNO center dot center dot center dot O-3 complexes at these computational levels. The BSSE corrected interaction energies are in a range between 9 and 14 kJ mol (1) at the MP2/aug-cc-pVTZ computational level. The atoms in molecules (AIM) theory was also applied to explain the nature of the complexes. The interaction energies have been partitioned with the Natural Energy Decomposition Analysis (NEDA) showing that the most important attractive term corresponds to the charge transfer one. (C) 2009 Elsevier B.V. All rights reserved.