MOLECULAR-INTERACTIONS WITH ICY SURFACES - INFRARED-SPECTRA OF CO ABSORBED IN MICROPOROUS AMORPHOUS ICE

Spectroscopic effects produced by small molecules absorbed within the micropores of amorphous ice have been examined for ethylene oxide, CF4, and carbon monoxide in an effort to characterize the interaction of CO with the ice surface. The absorption of CO at temperatures above 28 K produces a large shift (44 cm-1) in the position of the infrared bands of the dangling OH bonds at the pore surfaces and results in two distinct stretching-mode bands for the carbon monoxide, with one of the bands having an unusually high-frequency position (2152 cm-1). The influence of the absorbed small ether, ethylene oxide, was predictable as the dangling-bond bands of the ice "disappear", presumably because of an H-bond interaction with the absorbed ether. Because of this blocking of the dangling groups, the absorption of carbon monoxide into amorphous ice containing preabsorbed ethylene oxide (17%) occurs without interaction with the dangling bonds. Since the band at 2152 cm-1 is very weak in this case, it is assigned to CO bonded to the dangling OH groups. This assignment is supported by the observation that coabsorption with the hydrophobic gas CF4, which has only a minor influence on the spectrum of the dangling OH groups and which is expected to cause preferential association of coabsorbed CO with the dangling OH groups, enhances the relative intensity of the 2152-cm-1 band.