The formation and decay processes of CH3NH3(CH3NH2)(n) produced by the photolysis of (CH3NH2)(n) are studied by a pump-probe technique with femtosecond laser. The dissociation time of CH3NH2 in clusters is estimated to be less than 500 fs, while the formation time of CH3NH3(CH3NH2)(n) is less than 2 ps in the photolysis at 200 nm. The lifetime of free CH3NH3 is determined to be 30 ps and is elongated by 10(5) times in clusters. The ionization potentials and the binding energies of these clusters are determined by photoionization threshold measurements. On the basis of these results, the formation and decay processes for these clusters are discussed. (C) 2004 Elsevier B.V. All rights reserved.