Adsorption of small molecules on amorphous ice: volumetric and FT-IR isotherm co-measurements: Part II. The case of CO

The aim of this paper is to deepen the investigation of vibrational properties of CO adsorbed on amorphous ice, by using the combination of volumetric and spectroscopic isothermal measurements as presented in part I. CO is found to be one of the more interactive molecules that can be physisorbed on ice, as proved by the sharp increase in the adsorbed amount at the monolayer formation. The analysis of the evolution of the infrared signals as a function of equilibrium pressure, for both ice and CO, allows us to elucidate the origin of the peak at 2139 cm−1 as due to CO–CO interactions and to characterize the evolution of the three ice surface signals. Pre-adsorbing CF4 or CH4 enables site selectivity to be evidenced, CO being preferentially associated to dangling O–H bonds.