The kinetics of the successive ligand substitutions in the Fe(CO)(n)(+)/H2O systems (n=1-5) are studied using a triple cell Fourier Transform Ion Cyclotron Resonance spectrometer. For n=3 and 4, substitution of the last ligand is not observed and the terminal substitution products are Fe(CO)(H2O)(n-1)(+); a second channel in which two CO are simultaneously replaced by a H2O molecule is also observed. The internal energy of the Fe(CO)(n)(+) ions has no significant effect on the reactivity. In the Fe(CO)(2)(+)/H2O system, the second substitution shows a marked negative dependence with the energy of the reacting Fe(CO)(H2O)(+) ions, as confirmed by a quantitative study of the effect of a variable argon pressure in the reaction cell. (C) 2002 Elsevier Science B.V. All rights reserved.