  Using the multipolar expansion of the electrostatic energy, we have
characterized the asymptotic interactions between an oxygen atom O$(^3P)$ and
an oxygen molecule O$_2(^3\Sigma_g^-)$, both in their electronic ground state.
We have calculated the interaction energy induced by the permanent electric
quadrupoles of O and O$_2$ and the van der Waals energy. On one hand we
determined the 27 electronic potential energy surfaces including spin-orbit
connected to the O$(^3P)$ + O$_2(^3\Sigma_g^-)$ dissociation limit of the
O--O$_2$ complex. On the other hand we computed the potential energy curves
characterizing the interaction between O$(^3P)$ and a O$_2(^3\Sigma_g^-)$
molecule in its lowest vibrational level and in a low rotational level. Such
curves are found adiabatic to a good approximation, namely they are only weakly
coupled to each other. These results represent a first step for modeling the
spectroscopy of ozone bound levels close to the dissociation limit, as well as
the low energy collisions between O and O$_2$ thus complementing the knowledge
relevant for the ozone formation mechanism.
