Gas phase hydrogen-bonded isomers of the O-3-HONO complex have been investigated by means of DFT(B3LYP), MP2, MP4(SDTQ), CCSD(T) and QCISD(T) methods in conjunction with the 6-311++G(2d, 2p), 6-311++G(df,pd), AUG-cc-pVDZ and AUG-cc-pVTZ basis sets. Ten isomers were found for the O-3-HONO complex. The O center dot center dot center dot H and O center dot center dot center dot O interactions are predicted that participate in the formation of non-planar ring structure of the most stable isomer. The AIM calculations reveal that the O center dot center dot center dot H interaction in the most stable complex is stronger than others. In addition, both O center dot center dot H and O center dot center dot center dot O interactions in O-3-HONO complexes are electrostatic in nature. (C) 2009 Elsevier B. V. All rights reserved.