A study of the interaction of CO with water ice

¹ Instituto de Estructura de la Materia, CSIC, Serrano 123, 28006 Madrid, Spain e-mail: rescribano@iem.cfmac.csic.es
² Instituto de Astrofísica de Andalucía, CSIC, Aptd. 3004, 18080 Granada, Spain

Received: 6 March 2007
Accepted: 4 June 2007

Abstract

Aims.We studied the interaction between CO₂ (guest) and H₂O (host) molecular ices.

Methods.Ices of CO₂ and H₂O are prepared by four different 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 different varieties of association of CO₂ and H₂O are revealed from the different spectroscopic properties of the asymmetric stretching band of ¹²CO₂ and ¹³CO₂. 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 ( kJ mol^-1) and crystalline ( 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.