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.

In Figure 8, two spectra shown as (a) and (b) are permutated with each other. The text and the figure caption are correct, so the two spectra must be exchanged with each other.