The pick-up technique has been employed to deposit single ammonia molecules as chromophores on the surface of large ATN clusters and to create small ammonia complexes attached to host clusters. Mass spectrometric investigations have been carried out to characterize the pressure dependence of the guest cluster formation. The technique is then combined with molecular beam depletion spectroscopy employing the infrared radiation of a pulsed CO2 laser. In the region between 920 and 1060 cm(-1) in which the nu(2) bending vibration (umbrella mode) can be excited, absorption spectra have been measured for the ammonia monomer as well as for the ammonia dimer, trimer, and tetramer adsorbed on large ATN host clusters. For the monomer a significant blue shift of 14.74 cm(-1) is observed. Furthermore, it is found that the inversion motion associated with the umbrella mode is appreciably perturbed, resulting in a reduction of the inversion splitting by a factor of 0.3. As in the argon matrix, the rotation is only slightly hindered. The absorption spectra measured for ammonia dimers, trimers, and tetramers resemble very much the gas phase spectra of these complexes, except that they are blue shifted by 17 (dimer) and 6 cm(-1) (trimer and tetramer). From this close resemblance it is concluded that the structures of the small ammonia complexes are not affected by the argon host cluster.