The structure of the O₂-N₂O complex

We have investigated the lowest energy structures and interaction energies of the oxygen nitrous oxide complex (O₂–N₂O) using explicitly correlated coupled cluster theory. We find that the intermolecular potential energy surface of O₂–N₂O is very flat, with two minima of comparable energy separated by a low energy first order saddle point. Our results are able to conclusively distinguish between the two sets of experimental geometric parameters for O₂–N₂O that were previously determined from rotationally resolved infrared spectra. The global minimum structure of O₂–N₂O is therefore found to be planar with a distorted slipped parallel structure. Finally, we show that the very flat potential energy surface of O₂–N₂O is problematic when evaluating vibrational frequencies with a numerical Hessian and that consideration should be given as to whether results might change if the step-size is varied