A combination of GGA total-energy calculations and vibrational spectra simulations with HREELS experiments is reported to obtain new insights in the stable adsorption modes of the acrolein molecule on the Pt(I 11) surface. The simulations of the EELS spectra have allowed us to interpret the evolution of the experimental spectra, as a function of gas exposure. A strongly bound and coverage dependent chemisorption structure is shown. The I L spectrum has been assigned to a low coverage eta(3)-cis and eta(4)-trans mixed phase, with the molecule lying flat on the surface and interacting by both C=C and C=O bonds. The modified spectrum for an exposure of 2 L is associated with a change in the molecule adsorption structure toward a high coverage eta(2)-cis and eta(2)-trans form on the surface in complete agreement with the DFT total energy results.