The terahertz spectrum of 7-azaindole in solution has been obtained from 5 to 165 cm(-1) and analyzed using density functional theory calculations. The experimental spectrum exhibits a strong absorption feature at 76 cm(-1) that is attributed to an intermolecular vibration of self-associated 7-azaindole dimers. The calculations reveal that observed spectral features, which are unaccounted for in the 7-azaindole dimer normal mode analysis, may be attributed to a 7-azaindole hydrogen-bonded tetramer. This work presents the first quantum mechanical investigation of the structure and low-frequency vibrational motions of the 7-azaindole tetramer. (c) 2006 Elsevier B.V. All rights reserved.