Quantum mechanics of molecular oxygen clusters: rotovibrational dimer dynamics from realistic potential energy surfaces

Abstract

The three low-lying potential energy surfaces in the O₂–O₂ dimer, describing the dependence of the interaction on the intermolecular distance and on the relative molecular orientation, had been accurately characterized from the analysis of scattering experiments carried out by using polarized O₂ beams, generated and selected under angular and velocity resolution conditions suitable to measure quantum interference effects in the velocity dependence of the integral cross sections. Most of the bonding in the dimer was found to come from van der Waals forces, but in this open shell-open shell system chemical (spin–spin) contributions, to the ground state interaction at the equilibrium, are ∼15%. This complete characterization of the potential energy surfaces, of interest also for the theory of weak chemical bond and crucial to define structure, dynamics and spectroscopic features of the complex, is exploited in this paper to calculate the bound rotovibrational states for the O₂–O₂ dimer for J ⩽ 6 by solving a secular problem over the exact Hamiltonian, considering O₂ monomers as rigid rotors, and where the Coriolis coupling is included, allowing the assessment of the limits of the centrifugal sudden approximations. The results of this study are of relevance for the analysis of spectra and the description of characteristic internal motions for this prototypical weakly bound molecular complex.