1National Institute of Information and Communications Technology, Nukui-kita, Koganei, Tokyo, 184-8795, Japan
2Department of Chemistry, Tokyo Metropolitan University, Hachioji, Tokyo, 192-0397, Japan
3Department of Basic Science, Graduate School of Arts and Sciences, The University of Tokyo, Komaba, Meguro-ku,Tokyo 153-8902, Japan
*present address: Japan Agency for Marine-Earth Science and Technology (JAMSTEC) Showa-machi, Kanazawa-ku, Yokohama-city, Kanagawa, 236-0001, Japan
**present address: Department of Chemistry and Chemical Biology, Graduate School of Engineering, Gunma University,4-2 Aramaki, Maebashi, Gunma 371-8510, Japan
Abstract. Until recently, abundance estimates for bound molecular complexes have been affected by uncertainties of a factor 10–100. This is due to the difficulty of accurately obtaining the equilibrium constant, either from laboratory experiments or by statistical thermodynamic calculations. In this paper, we firstly present laboratory experiments that we performed in order to determine the molecular structure of H2O-O2. We also derive global abundance estimates for H2O-O2 in the Earth's atmosphere. The equilibrium constant Kp evaluated using the "anharmonic oscillator approach" (AHOA) (Sabu et al., 2005) was employed: the AHOA explains well the structure of the complex obtained by the present experiment. The Kp calculated by this method shows a realistic temperature dependence. We used this Kp to derive global abundance estimates for H2O-O2 in the Earth's atmosphere. The distribution of H2-O2 follows that of water vapour in the troposphere and seems inversely proportional to temperature in the lower stratosphere. Preliminary estimates at the surface show amount of H2O-O2 is comparable to CO or N2O, ranking water vapour complexes among the ten most abundant species in the boundary layer.