In this paper we describe a series of beam-surface scattering experiments which examine the internal and translational energy dependence of the molecular condensation probabilities for CCl4 or SF6 colliding with their respective condensed phases. It has been conclusively shown that thermal excitation of a polyatomic molecule’s rotational and vibrational degrees of freedom can inhibit its probability of sticking upon impact with a cryogenically cooled surface. This effect is most pronounced in the limit of low incident kinetic energy, and essentially vanishes at higher velocities. As part of these experiments; we have also obtained the angular and velocity distributions for reflected SF6 and Kr which have been used to examine the energy and momentum exchange of these gases with their respective condensed phases. Our findings suggest that heterogeneous laser isotope separation schemes based on precollision molecular excitation may warrant further investigation.