Is the iodide and persulfate reaction bimolecular?

Given the following reaction in an aqueous state:
$$ \mathrm{2I^- + S\_2O\_8^{-2}\rightarrow I\_2 + 2SO\_4^{2-}}$$
Is it bimolecular o trimolecular? Because two molecules of iodide react with one molecule of persulfate, so I would say trimolecular. 
Furthermore, I know it is a second order reaction because of the Iodide Clock experiment I performed, so would that mean that the reaction is complex and not an elementary reaction?


