Correlated ab initio study of the ground electronic state of the O2-HF complex.

In this paper, we present the first correlated ab initio investigations on the ground electronic state of the O(2)-HF complex. Calculations were performed using the CCSD(T) method with the aug-cc-pVDZ and aug-cc-pVTZ basis sets. The results show that there are two equivalent minimum energy hydrogen-bonded structures of planar bent geometry, where the minima correspond to exchange of the oxygen atoms. For each minimum the length of the O-H hydrogen bond is 2.16 A. The best calculated value of D(e) of the equivalent minima is 271 cm(-1). The T-shaped geometry of the complex, with oxygen perpendicular to the axis connecting the center of masses of O(2) and the HF molecule, represents a barrier to tunneling between the equivalent minima. The best estimated value of that barrier height is 217 cm(-1). The linear O-O-HF geometry of the complex represents a saddle point. The calculated geometrical parameters of the minimum energy structure of the complex are in reasonable agreement with the previously reported spectroscopic results. However, results of the current calculations suggest that a full understanding of the fine structures of the observed infrared spectrum of the complex requires the development of an effective Hamiltonian that takes the effects of tunneling into account.