The (O-2-HCI)(+) complex has been investigated theoretically in the doublet and quartet states. Equilibrium structures have been calculated at the CCSD level of theory with the aug-cc-pVDZ and 6-311++G(2d,2p) basis sets. One non-planar and two planar complexes are found in the doublet and quartet states, respectively. The doublet state complex is predicted to possess the largest interaction energy and be the most stable. Natural bond orbital analysis revealed intermolecular charge transfers occur followed by intramolecular charge rearrangement. The calculated vibrational frequencies are compared with those observed in solid Ne. (C) 2004 Elsevier B.V. All rights reserved.