Energy analysis of molecular ions (N-2(+) and CO+) scattered from Pt(111) was performed at an incident energy of 30 eV as a function of the scattering angle with a newly developed ion scattering apparatus. The kinetic energy of surviving molecular ions of N-2(+) and CO+ is quite different from that expected for the united-atom approximation of molecular ions with a mass of 28 and is higher than the estimated kinetic energy. The surviving molecular ions are scattered from the surface in a manner different from atomic ions. The angular distribution for both molecular ions is strongly shifted away from the specular direction toward the surface, as expected for the reactive ions. The small difference in the angular distribution between N-2(+) and CO+ can be understood as a result of the polarization of the heteronuclear molecular ion of CO+.