Context. Ice photodesorption has been the topic of recent studies that aim to interpret the abundances of gas-phase molecules, in particular CO, toward cold interstellar regions. But little is known about the effect of the ice’s physical properties on the photodesorption rate. The linear decrease observed in the photodesorption rate, as a function of increasing CO ice deposition temperature, was provisionally attributed to a more compact CO ice structure.
Aims. The goal of this work is to monitor the physical properties of solid CO as a function of ice deposition temperature. Then, we evaluate the possible link between the structure of ice and the ice’s photodesorption rate.
Methods. Infrared spectroscopy is an efficient tool to monitor the structural evolution of pure ices during warm-up or irradiation. The infrared absorption bands of molecular ice components observed toward various space environments allow for the detection of H2O, CO, CO2, CH3OH, NH3, etc. Typically, a pure ice that is composed of one of these species displays significant changes in their mid-infrared band profiles as a result of warm-up. But, at most, only very subtle changes appear in the narrow CO ice infrared absorption band as the result of warm-up. We, therefore, also used vacuum-ultraviolet spectroscopy of CO ice to monitor the effect of temperature in the physical properties of the ice. Finally, temperature-programmed desorption and photo-desorption experiments for different CO ice deposition temperatures were performed.
Acknowledgments
We are very grateful to the group of M. A. Satorre, from Universitat Politècnica de València in Alcoi, for sharing their results prior to publication. This work has been supported by the Spanish MINECO under projects AYA2011-29375, AYA2014-60585-P, and CONSOLIDER grant CSD2009-00038. We also benefited from financial support by MOST grants in Taiwan: MOST 103- 2112-M-008-025-MY3.
