Li+ ion attachment mass spectrometry was used to determine the ionic and neutral chemical components of a flowing microwave (MW) discharge plasma of H2O. The plasma composition was investigated as functions of H2O (in helium) flow rate (pressure) and MW-induced power input. Our study clearly showed the presence of various clustering compounds of water as well as their ionized species. Among compounds are the interesting ionic series H3O- (H2O)(n)O (n = 0-2) and (H2O)(n)O+ (n = 0-4), which have not been reported before, We consider the reaction schemes for some products, particularly with regard to the role of radical and ionic condensation reaction processes. We attempted to link both the ionic and neutral species to a mechanism. Our predictions indicate that. for example, the principal ionic condensation reaction can be summarized by the reaction sequence H3O- (H2O)(n)X + H2O --> H3O+ (H2O)(n+1)X (X = O, OH), while involving the OH radical may lead to the formation of (H2O)(n)Li+ OH adduct species. (C) 2002 Elsevier Science B.V. All rights reserved.