Exchange interaction between two O2 molecules using the asymptotic method

Abstract

The interaction between two O2(3Σ−g) molecules gives rise to three dimer states with spin quantum number S=0, 1, and 2. The splitting between the spin states is accurately represented by the Heisenberg Hamiltonian. Using the asymptotic method, an analytical expression for the exchange coupling parameter J is proposed. Such an expression, easily handable, furnishes a straightforward understanding of the behavior of J with the O2–O2 intermolecular separation, R. In the present paper, we have evaluated the exchange coupling parameter in a wide range of orientations of the monomers for various fixed values of R. Analytical expressions of J are given for various specific geometries in terms of a polynomial in (1/R) multiplied by an exponential part with an exponent of 3.6 Å−1. Results are compared with experimental data and previous ab initio computations. A rather good qualitative agreement is found with ab initio calculations in the selected range of orientations and distances.