Sub-monolayer coverages of CO on water ice

The adsorption of carbon monoxide (CO) at sub-monolayer coverages on water ice films vapour deposited on gold at a range of temperatures in ultrahigh vacuum has been investigated using reflection-absorption infrared spectroscopy. Evidence is presented from the interpretation of these data as to the nature of the binding sites for CO on the water ice surface. The results may have consequences for the interpretation of astronomical spectra.