Theoretical Study of O2−H2O:  Potential Energy Surface, Molecular Vibrations, and Equilibrium Constant at Atmospheric Temperatures

The intermolecular potential energy surface of O2−H2O was investigated at ab initio MP2 and MRSDCI levels using the aug-cc-pVTZ basis set. The vibrational levels were evaluated by numerically solving the Schrödinger equations for the nuclear motions with the ab initio potential functions using one- to three-dimensional finite-element methods. On the basis of the calculated partition functions, the equilibrium constant of the complex, K p, was studied. The K p values at atmospheric temperatures of 200−300 K were found to be 1−2 orders of magnitude less than previous estimates from the harmonic oscillator approximation.