A study of the interaction of CO2 with water ice

Aims. We studied the interaction between CO2 ( guest) and H2O ( host) molecular ices. Methods. Ices of CO2 and H2O are prepared by four di ff erent deposition techniques: sequential deposition ( amorphous water ice followed by addition of CO2), co- deposition ( both gases added simultaneously), inverse sequential deposition ( carbon dioxide ice followed by addition of water) and crystalline sequential deposition ( crystalline water ice is prepared first and CO2 is added afterwards). Samples are deposited at 80 K and are studied by temperature programmed desorption and transmission infrared spectroscopy. Results. Two slightly di ff erent varieties of association of CO2 and H2O are revealed from the di ff erent spectroscopic properties of the asymmetric stretching band of (CO2)-C-12 and (CO2)-C-13. The two varieties are found to co- exist in some of the samples at 80 K, whereas only the so- called internal CO2 remains after heating at 105 K. At 80 K carbon dioxide is able to adhere to a crystalline water ice surface. Activation energies for the desorption of CO2 from amorphous ( Ed = 20 : 7 +/- 2 kJ mol (-1)) and crystalline ( Ed = 19 : 9 +/- 2 kJ mol(-1)) water ice are derived from measurements of the sticking of CO2 as a function of ice temperature. Conclusions. These findings may have implications for the study of icy bodies of the Solar System.