We report vibrational predissociation spectra and theoretical analysis of the Ar-tagged cluster ions of imidazole, Im(1-3)H(+)center dot Ar. The frequencies of the external N-H stretches are observed to incrementally blue-shift toward that of neutral imidazole upon addition of the second and third Im molecules, consistent with the calculated behavior of the Im(3)H(+) complex in which the excess charge is symmetrically shared by two internal N-H-N hydrogen bonds. A very strong, symmetrical doublet near 1000 cm(1) is observed for the Im(2)H(+) complex and attributed to the parallel bridging proton displacement based on anharmonic frequency calculations. (C) 2010 Published by Elsevier B.V.