Vibrational predissociation spectroscopy and theory of Ar-tagged, protonated Imidazole (Im) Im1–3H+·Ar clusters

We report vibrational predissociation spectra and theoretical analysis of the Ar-tagged cluster ions of imidazole, Im1–3H+·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 Im3H+ 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 Im2H+ complex and attributed to the parallel bridging proton displacement based on anharmonic frequency calculations.