Our previous model on dimer sputtering is extended to the formation of larger clusters. The general formalism for the calculation of the momentum distribution function of these clusters is given. A simple analytical expression is obtained for the distribution function of any cluster in the high energy limit. Comparison of this expression with experimental data on the energy and angle distribution of Wk+clusters at high energies shows good agreement. The experimental results on K2and KI sputtering with low energies are recompared with the theory. For the ionic crystal KI, evidence is obtained that sputtering of non adjacent K and I atoms from the lattice gives an important contribution to dimer formation. The role of the binding energyEb, of the particles with respect to the surface is discussed.