Theoretical study of O2-H2O:: Potential energy surface, molecular vibrations, and equilibrium constant at atmospheric temperatures

The intermolecular potential energy surface of O(2)-H(2)O 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 Schrodinger 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.