Experimental results are presented for the scattering of well-defined beams of molecular oxygen incident on clean Al(111). The data consist of scattered angular distributions measured as a function of incident angle, and for fixed incident angle, the dependence on, surface temperature of the angular distributions. The. measurements are interpreted in terms of a scattering theory that treats the exchange of energy between the translational and rotational motions of the molecule and the phonons of the surface using classical dynamics. The dependence of the measured angular distributions on incident beam. angle and temperature is well explained by the,theory. Rotational excitation and quantum excitation of the O-2 internal stretching mode are briefly discussed. (C) 2004 American Institute of Physics.