Argon predissociation spectroscopy is used together with ab initio electronic structure calculations to characterize the NO-.(H2O)(n=1-3) clusters. In all cases, the water molecules bind to the ion through single ionic H bonds. Two isomeric forms are assigned for the n=1 species that differ according to whether the H bond occurs to the N or O atom of the core ion. While the spectra of the dihydrate indicate formation of an H-bonded water dimer subcluster consistent with all four predicted isomers, their calculated vibrational spectra are too similar to establish which of these forms is created in the ion source. Three classes of isomers are predicted for the NO-.(H2O)(3) clusters, and in this case a comparison of the experimental and theoretical infrared spectra indicates the formation of a bridging arrangement in which two of the water molecules are attached to one atom and the third to the other atom of NO-. This distorted water trimer motif is intermediate between the symmetrical trimer found in the X-.(H2O)(3) [X=Cl,Br,I] clusters and the open structure displayed by the O-2(-).(H2O)(3) system. The structural differences between the complexes of water with O-2(-) and NO- are discussed in the context of the relative proton affinities and the electronic structures of their ground states (i.e., (3)Sigma(-)NO(-) versus (2)Pi(g)O(2)(-)). Spectra of the NO-.(H2O)(4,5) clusters are also presented together with a qualitative discussion of the likely morphologies at play in these higher hydrates. (C) 2003 American Institute of Physics.