The adsorption of the cyclic ether trioxane, or trioxymethyklene (C3H6O3), has been studied on the (111)-oriented single crystal copper surface using photoelectron spectroscopy, thermal desorption spectroscopy and low energy electron diffraction. The large dipole moment of the molecule leads to a rather complex adsorption behaviour, three different adsorption regimes with different molecular orientation and binding energies are found. At all coverages molecular adsorption was observed, in the submonolayer regime trioxane adsorbs with the ring-plane parallel to the surface.