A first glimpse at the acidic proton vibrations in HCl–water clusters via supersonic jet FTIR spectroscopy

Abstract

The first mid-IR spectra of the proton vibrational dynamics in isolated HCl–water clusters are presented. Pulsed expansions of HCl and water in rare gases through a slit nozzle are probed by an FTIR spectrometer in the 2000–3300 cm⁻¹ range. Distinct absorptions by small HCl and HCl–water clusters are superimposed on broad bands, partly due to electrolytically dissociated HCl. A firm assignment of the 1 : 1 complex (at 2723.5 cm⁻¹) is provided together with a more tentative assignment of the 1 : 2 complex (near 2464 cm⁻¹). The results are compared to condensed phase, matrix isolation and theoretical studies as well as exploratory quantum-chemical calculations. A rationale for the low abundance of small molecular HCl–water clusters beyond the 1 : 1 complex is given.