A formalism is developed for modeling the interaction between a particle scattering from a surface and the thermal vibrations of the lattice, using the reduced density matrix. A short time propagation algorithm is constructed, with the dissipative terms derived directly from the full particle-bath Hamiltonian. The resulting Bloch-Redfield equation is used to study the scattering of He, Ne, and Ar from model Cu and Ru surfaces, over a wide range of energy and temperature. Trapping and desorption are also examined, and comparisons are made with experimental sticking data. The method is shown to give reasonable results and to accurately describe the relaxation to equilibrium over long times.