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.