Reactions of M+(H2O)(n), n < 40, M = V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, with D2O are studied by Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Isotopically highly enriched metals are used as applicable. Isotopic scrambling with formation of HDO is not observed for M = Cr, Fe, Co, Ni, Cu, and Zn, which indicates that these hydrated metal ions consist of a singly charged metal center and a hydration shell of intact, inactivated water molecules. In the vanadium case, HDO formation is observed in the size region where also hydroxide formation with evolution of molecular hydrogen occurs. For manganese, HDO formation occurs in the size regime n approximate to 8-20. Additional experiments show that, in this size regime, Mn+(H2O)(n) is slowly converted into HMnOH+(H2O)(n-1) under the influence of room temperature blackbody radiation. The reaction is mildly exothermic; Delta H approximate to -21 +/- 10 kJ mol(-1).