Scattering of electronically excited, state-selected metastable CO(a(3) Pi) molecules from a cleaved LiF(100) surface is studied experimentally. Internal state distributions, fluorescence profiles, time-of-flight (TOF) profiles and angular distributions of the surviving metastable CO molecules are measured. Relative and absolute survival probabilities are determined for various impact velocities. The dependence of translation and rotational temperature on the velocity of the incoming beam unambiguously indicates a direct inelastic scattering process, even though the angular distributions are broad, both in plane and out of plane. The internal state distribution after scattering shows an overpopulation of the initially prepared Omega=1-component relative to die other spin components.