The IR spectrum of 7-azaindole monomer, 7-azaindole reactive and nonreactive dimers, and (7-azaindole)(H2O)(n) (n = 1-3) clusters in a supersonic jet from 2600 to 3800 cm(-1) have been measured using IR dip spectroscopy. The vibrational transitions in the ground state were clearly observed and were assigned to the CH and NH stretching vibrations of 7-azaindole and the OH stretching vibrations of water molecules in the clusters. The observed IR spectra of 7-azaindole monomer and (7-azaindole)(H2O)(n) (n = 1-3) clusters were compared to theoretical ones obtained by ab initio MO calculations. From a comparison, it is concluded that (7-azaindole)(H2O)(n) (n = 1-3) clusters have a ring structure due to a cyclic hydrogen-bond network. This conclusion is consistent with an analysis based on high-resolution spectroscopy. Similarly, the IR dip spectrum suggests that the 7-azaindole reactive dimer has a cyclic hydrogen-bond network, forming a symmetric planar structure. It is strongly suggested from the IR spectrum and the ab initio calculations that the nonreactive dimer contains a water molecule between 7-azaindole molecules.