IR spectroscopy of pyridine–water structures in helium nanodroplets

Abstract

We present the results of an IR spectroscopic study of pyridine–water heterodimer formation in helium nanodroplets. The experiments were carried out in the frequency range of the pyridine C–H stretch region (3055–3100 cm⁻¹) and upon water deuteration in the D–O stretch region (2740–2800 cm⁻¹). In order to come to an unambiguous assignment we have determined the angle between the permanent dipole and the vibrational transition moment of the aggregates. The experiments have been accompanied by theoretical simulations which yielded two minimum structures with a 16.28 kJ mol⁻¹ energy difference. The experimentally observed bands were assigned to two structures with different H-bonds: an N⋯H bond and a bifurcated O⋯H–C bond.