The growth of ammonia cluster (NH3)(n) (n = 2-8) in He droplets was studied using a polarizable potential assuming ultrafast heat dissipation and preventing the rearrangement of cluster structures. Energies, structures and isomer statistical distributions were obtained showing that a few high energy isomers may form with a probability similar to low energy ones and that ammonia clusters behave differently from (H2O)(n) for n >= 5. Guide by our theoretical analysis, we suggest the need for re-interpreting recent experimental IR spectra of (NH3)(n) in He droplets for 5 <= n <= 8. (C) 2011 Elsevier B.V. All rights reserved.