Theoretical Characterization of the Gas-Phase O3HO Hydrogen-Bonded Complex

6 pages, 2 tables, 3 figures.We report a theoretical study on two gas-phase hydrogen-bonded complexes formed between ozone and hydroxyl radical that have relevance to atmospheric chemistry. This study was carried out by using CASSCF, CASPT2, QCISD, and CCSD(T) theoretical approaches in conjunction with the 6-311+G(2df,2p) and aug-cc-pVTZ basis sets. Both complexes have a planar structure and differ from each other in the orientation of the electronic density of the unpaired electron associated with the HO radical moiety. Our calculations predict their stabilities to be 0.87 and 0.67 kcal mol-1, respectively, at 0 K and show the importance of anharmonic effects in computing the red shift of the HO stretch originating from the hydrogen-bonding interaction. We also report two transition states involving the movement of the HO moiety on the potential energy surfaces of these hydrogen-bonded complexes.The financial support for this research was provided by the Spanish Dirección General de Investigación Científica y Técnica (DGYCIT, grant CTQ2005-07790) and by the Generalitat de Catalunya (Grant 2005SGR00111). The calculations described in this work were carried out at the Centre de Supercomputació de Catalunya (CESCA), whose services are gratefully acknowledged, and on an AMD Opteron cluster of our group. A.M. thanks the Spanish Ministerio de Educación y Ciencia for a fellowship (BES-2003-1352).Peer reviewe