The intermolecular potential energy surface of the ground electronic state of the O2-H2 complex.

This work presents the first high level correlated ab initio study of the intermolecular potential energy surface of the ground electronic state of the O(2) (X (3)Sigma(g)(-))-H(2)(X) complex. This computational study was carried out using the CCSD(T) level of theory with the aug-cc-pVXZ basis sets, where X = D, T, Q, and 5. All calculated energies were corrected using the BSSE method. The lowest energy geometry and the shape of the intermolecular potential energy surface showed significant dependence on the size of the basis set as well as the BSSE corrections. The most accurate results were obtained using the CCSD(T)/aug-cc-pVQZ and CCSD(T)/aug-cc-pV5Z combinations with the BSSE corrections. These calculations yield a global minimum of C(2v) symmetry, where internuclear axes of the O(2) and H(2) moieties are parallel to each other. For this geometry, the D(e) value is 65.27(30) cm(-1), which is in excellent agreement with the CBS limit of 65.14 cm(-1). The distance between centers of masses of the H(2) and O(2) monomers within the complex is 3.225(1) A. Barrier heights to rotation of the H(2) and O(2) units by 180 degrees about the axis that connects their centers of masses are 24 and 159 cm(-1), respectively. The current results should stimulate microwave spectroscopic detection of the O(2)-H(2) complex.