The scattering behavior of neutral ammonia clusters off a LiF(100) surface is studied. Ammonia clusters are produced by a coexpansion of NH and Kr with an average kinetic energy of 48 meV per monomer molecule. Using single photon VUV laser ionization at "118 nm (h "10.49 eV) the mass distribution of scattered particles is obtained in a reflecting time-of-flight mass spectrometer. Compared with the incoming cluster beam the average cluster size of the scattered particles is drastically decreased. The angular distribution of NH> and NH> after scattering reveals a strong inelastic interaction between the clusters and the LiF(100) surface which is described in the context of a thermokinetic model and a phonon excitation along the (001) azimuth of the LiF(100) surface.